Astronomy

How did Mars come to have a 24 hour 39 minute day?

How did Mars come to have a 24 hour 39 minute day?



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Mercury rotates three times for every two revolutions around the Sun, apparently due to a gravitational resonance with the Sun.

Venus takes about 225 days to rotate, and rotates in the opposite direction of any of the inner planets. Maybe because its extreme nature makes it ornery.

Earth rotates once every 24 hours, a condition caused by the tidal interaction between Earth and its Moon. It's believed that the Earth was rotating about once every 5 hours before the theorized collision with a Mars sized coorbiting object referred to as Theia.

Mars shows no signs of a similar collision. Its two moons appear to be asteroids that were captured from the asteroid belt. So how did Mars come to have a day so close to the length of an Earth day?


"It's believed that the Earth was rotating about once every 5 hours before the theorized collision with a Mars sized coorbiting object referred to as Theia."

Almost. Theia did not have to be co-orbiting, just an intersecting orbit. We have no idea what the Earth's spin was before the collision, but it is theorized that the Earth rotation had a 5 hour period after the collision with Theia, at the time of the Moon's formation from the debris.

The fact that Mars and Earth have such a similar period is a coincidence, perhaps you are asking why Mars is spinning so fast? Well actually Mars is not the odd man out, Mercury and Venus are. Most planets spin fast. exactly which spin orientation is somewhat arbitrarily determined by the vagaries of the ways the planetesimals collided to form them. The fact that Venus and Uranus have unusual spin orientations is just the way things turned out.

Both Mercury and Venus used to spin much faster. Mercury's spin was tidally slowed down by the Sun and Mercury's orbit was (and still is being) driven further away by the Sun (just like the Moon and Earth: Why is the Moon receding from the Earth due to tides? Is this typical for other moons?). Eventually Mercury was held in that 2:3 resonance. Which, by the way had a certain amount of luck involved (see: Mercury's capture into the 3:2 spin-orbit resonance as a result of its chaotic dynamics ). Venus, we are not so sure of.

The tidal force from the sun is much much less for Venus than for Mercury, but much more than for Earth. However Venus has a dense hot massive atmosphere, which can be forced into both gravitational bi-modal (two peaks) tides and thermal uni-modal (one peak) tides. The bulge lags behind the tidal forcing peak, which creates a torque by the sun to slow it down. This is fiendishly complex (See: Long term evolution of the spin of Venus - I. Theory )


P.S. Actually Phobos, and probably Deimos, are thought to be constructed fairly recently (millions of years) from debris from a collision of Mars with a large asteroid. There is no way to capture a whole asteroid into orbits that close.


How did Mars come to have a 24 hour 39 minute day? - Astronomy

Thus far, three categories of evidence have been cited concerning the former existence of a tenth planet, a small Pluto-sized body. Pluto's diameter is listed at 1,375 miles Astra's diameter may have been 200 miles greater. That tiny planet was on a collision course with Mars, and fragmented on Mars' Roche Limit. Its fragments created a hemisphere of craters, accounting for more than 85% of all of the Martian craters. But that fragmentation created something more.

The three categories of evidence on the fragmentation of Astra discussed to this point are (a) the gross imbalance in the uneven distribution of craters on Mars, (b) the giant Hellas Crater in the bulls eye zone of the Clobbered Hemisphere, and (c) the rim where the density of craters drops off markedly and obviously.

That tiny tenth former planet needs a name. In astronomy, by tradition, discoverers are given the privilege of naming their discovery(ies) The name "Astra" is hereby nominated it is cognate with asteroids, one of the main products of this fragmenting event. Also traditionally, the name of a new planet has come from Greek celestial mythology. Uranus, Neptune, Pluto.

In Chapter 6 there is a discussion of Greek mythology and the role therein of the Greek deity, Astra. Information there about Astra and her sojourn in the heavens will add a second reason to nominate the name "Astra."

The fourth in this series of clues isn't even in the Clobbered Hemisphere, where the Hellas Fragment hit. It is more or less opposite to the giant Hellas Crater, in the middle of the Serene Hemisphere. It is (d) the Tharsis Bulge.

The Tharsis Bulge of Mars geologically is considered to be a "shield" It is a bulge that is assessed by Moore and Hunt to be 5,000 km. (over 3,100 miles) broad. This diameter, if Moore and Hunt are correct, represents 23% of the circumference of Mars and 46% of the circumference of the Serene Hemisphere.

The height of the Tharsis Bulge is 23,000 feet above the surrounding plain. As it is with the Hellas Crater, the largest crater in this Solar System, so it is with the Tharsis Bulge. It, too, is the biggest bulge among the planets that have solid surfaces.

Evidence # 4 - The Tharsis Bulge

The giant Hellas Crater is located near to the center of the "Clobbered Hemisphere", or "Battered and Blasted Hemisphere." Apparently it was caused by a fragment almost the size of the largest asteroid, Ceres, which is 625 miles in diameter. The Hellas fragment created a huge crater, slightly elliptical, with a short diameter of 920 miles and a long diameter of 980 miles. In addition, the Hellas Fragment created a general indentation in the Clobbered Hemisphere.

Since Hellas Planitia is near the center of the Clobbered Hemisphere, this huge fragment must have hit Mars a direct blow, not a glancing blow. A foundation will be laid in a coming chapter to establish its velocity, 25,000 mph. This is 420 mp minute, and 7 mph second.

The crust of Mars is estimated at 20 miles thick, an opinion for which a foundation will be laid shortly. Thus the Hellas fragment penetrated entirely through the front crust of Mars, at a high velocity, and plowed into and almost through the fluid magma of Mars. It may be that the back crust, with a better angle of curvature, was what stopped the Hellas Fragment from going entirely through Mars.

Evidence will appear in a coming chapter indicating that both Astra and its fragments had spin rates, rapid spin rates, in addition to an orbital velocity of 25,000 mph. Depending on its diameters, the Hellas Fragment may have contained 25 to 50 million cubic miles of rocky material.

Once beyond the crust and into the hot magma soup of Mars, the Hellas Fragment created sudden, immense pressure waves. Pressure waves were in the front of the plunging Hellas. Shear waves were also involved they were perpendicular to the direction of the plunging Hellas. Thus the entire inside of the Serene Hemisphere suddenly suffered immense pressures. It bulged, apparently where the crust was the thinnest and the weakest.

The Tharsis Bulge is located within 30° of being opposite to the Hellas Crater. It probably represents the region in the Serene Hemisphere where the crust was thinnest and weakest. It was where the crust was first to yield to the new sudden immense pressure. The inner side of the crust of the Serene Hemisphere yielded up 23,000 feet, over 4 miles, which is the height of the bulge.

Thus, the Hellas Fragment was unable to pass clear through Mars, but it was able to do ample damage it suddenly thrust up the broad Tharsis Bulge. This bulge began to rise within 90 minutes of when Astra fragmented.

Moore and Hunt indicate the breadth of Tharsis is 3,100 miles, and its height is 23,000 feet above the surrounding terrain. (There is no mean sea level on Mars.) They describe the Tharsis Bulge as follows.

Mars is a small planet compared to the Earth. Its mass is only 10.7% of our planet's mass. Measuring from the Earth's sea level, the elevation of Tharsis exceeds all the peaks of the mighty Andes including Aconcagua, at 22,834 feet. The elevation of the Tharsis Bulge also exceeds all except the highest 22 peaks of the mighty Himalayas.

Were Tharsis on the Earth, its top would be in rarefied air. At 23,000 feet, three-fourths of the Earth's atmosphere is below. At 23,000 feet, barometric pressure is only 25% that of sea level. But Mars has no sea level and it has less than 1%, as much atmosphere as the Earth.

The Tharsis Bulge dominates the physical geography of the Serene Hemisphere of Mars. On it are the six largest volcanoes in the Solar System. The next six largest are in the region of the Elysium Bulge, the second bulge in the red planet's Serene Hemisphere.

The Probable Thickness Of The Crust Of Mars

Figure 4 illustrates the plunging Hellas Fragment. It encountered, successively, first the front crust of Mars, second, its hot magma interior, and perhaps third, its back crust. Crustal thickness on Mars is at issue in understanding both this bulge, and the giant volcanoes thereon. Its thickness indicates the resistance, of the front crust of the Hemisphere of the Clobbered Crust, to plunging large fragments like Hellas, Isidis, Argyre and also the smaller fragments. And it may indicate the resistance of the back crust of the Serene Hemisphere, denying Hellas a passage entirely through the red planet.

The crust of the Earth is considered to average ten to twelve miles in thickness. It is also considered to be elastic and flexible up to a point. It has an elastic-plastic threshold beyond which it will tear, but that threshold is never approached in this modern serene age.

The crust of Mars is considered to be thicker and more rigid, and much less elastic for several reasons. First, Mars is made of lighter materials than is the Earth. Earth's density is 5.52, Mars' density is 3.93 (and water is 1.0) The density of the crust of Mars is only 72% of the Earth's crust.

On Mars, as in the Earth's crust, temperatures rise going down vertically. But in going down, to where the temperatures can melt crust, temperatures rise only 70% as fast on Mars. Temperatures must rise to 3000° F. to liquefy the crustal materials such as silica and alumina.

Second, Mars is farther from the Sun by 52% than is the Earth. Hence its crust is colder at the beginning. Temperatures on the cold surface of Mars average -90° F. On a square mile to square mile basis, the surface of Mars receives only 43% as much radiation from the Sun as does the Earth. During the 24-hour 37-minute night, surface temperatures of -250° F. are common. So the surface of Mars has an average temperature of about 130° F. colder than the crust of our planet.

Third, Mars has almost no atmosphere. The Earth has an atmosphere that absorbs and retains a significant part of the heat that the Earth radiates to space. It is called captured radiation. The atmosphere of Mars captures very little radiation from the surface of Mars.

Fourth, Mars has only 55 million square miles of surface the Earth has 196 million. Thus, Mars has 28% as much surface as does the Earth, but it has only 11% as much mass as the Earth. Smaller planets with more surface per unit of mass radiate heat back into space more efficiently than do larger planets like the Earth and Venus.

This is why surface temperatures on Mars rise and plunge so rapidly, as much as 300° F. in a 24-hour period. At night, temperatures on Mars can drop 20+° F. per hour. Thus very cold temperatures penetrate to considerable depths in the crust of Mars. The crust of Mars is estimated to be 20 miles thick.

Fifth, the crust of Mars has a smaller radius of curvature than does the Earth's crust. Beyond the accelerated radiation factor, this gives the crust of Mars an added stiffness factor - a rigid inflexibility - that is not characteristic of the Earth's crust.

Thus Mars has both a thicker crust and a more rigid crust. Both features will make it more difficult for fragments of Astra to penetrate its crust than if they hit the surface of the Earth. However, it is clear that at least three fragments of Astra penetrated into the mantle of Mars, Hellas, Isidis and Argyre. Another ten or fifteen may have also. But most of the fragments under 100 miles in diameter didn't penetrate, even when hitting its crust at 25,000 mph.

The Location Of The Tharsis Bulge

The heartland of the Tharsis Bulge is located between 101 and 125° W. longitude. Our measurement is for breadth about 900+ miles. Our measurement for its length is from 16° N. to 12° S., making it over 1,000 miles. This makes its heartland area about 650,000 miles. For whatever reason, our measurements for the heartland of Tharsis are more conservative than those of Moore and Hunt for the entire bulge.

The evidence emerges that the Hellas fragment hit the crust of Mars a direct blow, from almost vertical. It passed into the internal magma of Mars, creating enormous pressure waves and shear waves. The Hellas Fragment did not pass out through the other side of the crust of the Serene Hemisphere. But the angle of the hit, its velocity, and the Hellas Fragment did cause sudden, immense internal distress, resulting in a huge pair of bulges in the opposite hemisphere.

Apparently the Hellas Fragment plunged into and through the crust and continued to plunge onward, rotating all the way, for up to three thousand miles through the magma of Mars. To describe the internal distress of Mars, it can only be said that it was beyond chaos cubed.

In the case of the Earth's atmosphere, shock waves have a velocity of about 750 mph. Sometimes they are called sonic booms. However velocities of pressure waves in the oceans are different in water they are four times as fast, 3,000 mph. Presumably, pressure waves in the magma of Mars were around 3,000 mph.

If so, the fragments of Astra hit the front crust some 11 or 12 minutes after Astra fragmented. The pressure waves, at an estimated 3,000 mph, required another 80 or 85 minutes to arrive at the Tharsis Bulge. Thus, the Tharsis Bulge began to rise, with suddenness, about 100 minutes after Astra fragmented.

The crust and the magma of Mars first had to slow down the speeding, plunging "H" fragment from 25,000 mph. Then its magma had to deal with the pressure waves and shear waves which the "H" fragment produced.

Simultaneously there were at least two other fragments that penetrated through the Martian crust, Isidis and Argyre. In the vicinity opposite the Isidis Crater is the second bulge of Mars, known as the "Elysium Bulge." It also contains a spread of volcanoes, huge by Earth's standards, but small by the standards of the volcanoes on Tharsis.

Thus the internal distress within Mars after Astra fragmented was "chaos cubed" It is beyond mathematical analysis. It was a wild and woolly day for the both the crust and the magma of Mars.

The Serene Hemisphere And The Elysium Bulge

The Isidis Crater is not far from the Rim of Craters on Mars in its Northeast Quadrant. Isidis is the second largest crater on Mars. This crater has a diameter of 450 miles and an area of 175,000 miles. The area of the Isidis' crater is equal to that of California, with Maryland and New Jersey added in for good measure. This is on a much smaller (and colder) planet.

Not far from the Isidis crater, and also in the Serene Hemisphere, is the Elysium Bulge on Mars. Like Isidis, the second-largest crater, Elysium is the second largest bulge on the red planet.

The Argyre Crater, the third largest, is about 300 miles in diameter, and contains some 75,000 sq. miles. Its area is equal to the state of South Dakota. Or, on the Eastern Seaboard, it is equal to the combined area of Delaware, the District of Columbia, Long Island, Maryland, New Jersey, Virginia and half of West Virginia. Where these two bulges are is an indication of where the thinnest parts of the crust of Mars are.

Figure 4 - - The Plunges of the Three Largest
Fragments of Astra (Hellas, Isidis and Argyre)

When Astra fragmented, and planetary catastrophism came to the planet Mars, it came in a fast, fierce, furious flurry. Similarly, when planetary catastrophism came to the planet Earth, it also came fast, fierce and furious. The calculations are that the fragments of Astra approached Mars at 25,000 mph. By comparison it calculates that Mars approached the Earth at a velocity differential of 30,000 mph.

The following is a citation about quaking, shaking and crustal deformation on another planet, the Earth, within the recorded memory of mankind. It was about 3,700 years ago, not 3,700 millions of years ago.

Each story in this skyscraper of catastrophic cosmology indicates a new understanding for a puzzling feature in this Solar System. Story 6 is the story of THE SUDDEN UPLIFTS OF THE THARSIS BULGE AND THE ELYSIUM BULGE ON MARS. Rising within a matter of a few hours, it was in no sense a gradualistic uplift.

A study of pressure waves and shear waves suggests Tharsis was beginning to be uplifted approximately 85 minutes after the gigantic Hellas Fragment blasted through the crust of Mars on the opposite side.

Simultaneously the Elysium Bulge was uplifted. Both of these regions of uplift probably reflect where the crust of Mars in the Serene Hemisphere was thinnest and weakest. They could least endure internal pressure and shear waves. The fact that both of these regions, and only these two regions also contain the volcanoes of Mars underlines that here, the crust of Mars was and is the thinnest and weakest.

The "H" Fragment, still rotating, first plunged through the 20-mile thick, rigid crust of Mars, which reduced its velocity somewhat, but not enough. Next its velocity was reduced by plunging through the 4,000 miles of the molten magma of Mars.

Finally the "H" Fragment came to a standstill by resistance of the underside of the crust of the Serene Hemisphere on the opposite side. Even then it was still rotating a bit. The suddenness, the immensity and the velocities of the two fragments were what created the two bulges. The dating of the fragmenting of Astra is touched upon several times in the following chapters. It was not 3.0 to 3.5 billion years ago.

Under the circumstances, it is not surprising that bulges developed suddenly in the Serene Hemisphere. Crustal bulging was one major method, but not the only major method in the process of relief for sudden, internal distress of Mars, an internal distress that suddenly gripped its inward regions. Volcanism also helped (see Chapter 4.) Rifting helped even more (see Chapter 3).

A. B. Guthrie of Choteau, Montana, a famous author of Western Americana, described the crest of the Rocky Mountains or the Continental Divide, as being "high, wide and handsome." Much higher, wider, and more handsome are the Tharsis and the Isidis Bulges on Mars.

With story 6, the reader now is 33% of the way to the penthouse. Each story provides a new insight for cosmology, the history of the Solar System, and each story provides an increasingly broad view of the human history on this planet.


How would I coordinate meetings with people on Mars?

First off, assume faster-than-light communication exists and has enough bandwidth to do video conferencing. This question wouldn't even be relevant without faster-than-light communication since it takes 3-22 minutes for a message to transmit at the speed of light between Earth and Mars and you can't have a coherent meeting with that kind of latency.

The problem here is that the Martian Sol is 37 minutes longer than it is on Earth. While they could simply go by Earth time*, and probably would keep an Earth clock if they needed to coordinate with Earthlings, many of the people prefer local time since it better matches natural sleep cycles and have adopted local time because the majority of people there don't interact much with Earth. As a result, Martian time essentially behaves like a timezone which shifts in and out of sync with Earth time.

This makes coordinating meetings across planets troublesome, to say the least. A meeting held during reasonable business hours on a weekday one week (assuming both operate on 7-day weeks) might be during breakfast for the Martians next week. After roughly 4 weeks on Earth, Mars is a whole day behind Earth, so Earth is trying to hold a Monday meeting while Mars is enjoying a lazy Sunday.

How do I, the CEO of Megacorp Industries, hold meetings with my Martian executives?

*Obviously, the problem is pretty much irrelevant if people go by Earth time, which would be reasonable to expect if they lived in controlled environments. The "Just use Earth time" also isn't necessarily going to make sense if this concept were to be generalized to some distant planet that is naturally habitable.


Two of Your Earth Minutes

In Speculative Fiction, Aliens Speaking English or aliens speaking through Translator Microbes will sometimes be heard to use terrestrial measurements, but will for some reason feel the need to emphasise that they are your units of Earth measurements, and not theirs. This implies that the extraterrestrials have their own units of measurement, that by improbable coincidence share a name with the ones humans use, but are otherwise different. Of course, this is rather like someone from a country which uses imperial measurements visiting one that uses metric ones and using phrases like "20 of your kilometers" or "6 of your kilograms". It also spares the audience from clunky exposition where the alien explains that a floob is equal to 2.837 meters.

When two civilizations with different home-worlds (and thus different years, hours, and so on) interact, referring to "your" time units or "(planet name) time units" is entirely correct. It's the redundancy of using both "your" and the name of the planet which makes this an awkward phrasing.

Happens to some degree in real life, in situations such a Brit talking to an American about "two of your gallons" - but this is exactly because Britain and the US use the same word to mean different volumes. (1 Imperial gallon == 1.2 American gallons). Likewise, just as "minute" comes from the Latin for a small division, the aliens may have a time unit named after their word for a small division. But if not, there is little point specifying that it is an 'Earth Minute'. Unless it's mocking or derogatory, like most real-life uses of the trope in metric vs. imperial situations. "Your years" makes more sense as the duration of a planet's orbit around its sun would be different for each world.


How our view of Mars has changed

Over centuries of gazing at Mars, research has changed our vision of the planet multiple times.

The dusty-red sphere now called Mars has fascinated stargazers since the dawn of humanity, but Earthlings' view of the planet has changed drastically over the years. Once thought of as a lush alien world teeming with life, it was later dismissed as an arid, desolate orb. But now, scientists have announced the Red Planet has long, fingerlike strips of seeping, salty, liquid water that just might aid in the search for extraterrestrial life.

The finding, revealed Monday (Sept. 28) by NASA scientists, once again changes the way people view the bright-red planet, Mars experts told Live Science.

The ancient Greeks and Romans named Mars — a planet barely more than half Earth's size — after the god of war. But they likely didn't realize it was another world, with two moons to boot, said Bruce Jakosky, a professor of geological sciences at the University of Colorado Boulder. [In Photos: Is Water Flowing on Mars?]

In the 1600s and 1700s, astronomers tinkered with nascent telescopes and discovered that Mars, like Earth, was a planet and had a roughly 24-hour day-and-night cycle. At this time, people assumed intelligent beings were scampering over the Martian surface, Jakosky said.

Early astronomers had other fanciful, and often mistaken, views of Mars. In 1784, the British astronomer Sir William Herschel wrote that the dark areas on Mars were oceans, and the light areas land. He also speculated the planet was home to aliens, who "probably enjoy a situation similar to our own," according to NASA. (He also apparently thought intelligent life was living under the sun's surface in a cool spot, NASA reported.)

As Kamala Harris’ portfolio grows, so does the scrutiny

In 1877, Italian astronomer Giovanni Schiaparelli reported seeing grooves or channels on Mars with his telescope. Schiaparelli called these features "canali," which can mean "natural channels" in Italian. The word was mistakenly translated into "canals" in English, a phrasing that suggested handiwork by living beings. American businessman and astronomer Percival Lowell popularized the idea, and wrote three books about aliens that likely created the canals to survive on a drying planet.

"The canals were an attempt, [Lowell] thought, by intelligent beings to carry water from the poles, where there was water, to the rest of the planet," said Richard Zurek, chief scientist for the Mars Program Office at NASA's Jet Propulsion Laboratory in Pasadena, California.

It wasn't until NASA's Mariner space missions in the 1960s and 1970s that researchers could confidently prove there were no alien-made canals, Zurek said.

"We almost went to the other extreme, because we saw a hilly, cratered landscape on the first flybys of the planet," Zurek told Live Science, referring to the Mariner 4 mission. "That suggested it was more like the moon than it was like the Earth."

Until then, scientists had speculated that Mars had a thick atmosphere that could trap heat and help the planet support life at its distant location from the sun. Mars orbits at about 142 million miles (229 million kilometers) from the sun, compared with Earth's 93-million-mile (150 million km) leap from the sun. But this wasn't the case Mars' atmosphere is about 100 times thinner than the gas layer surrounding Earth, partially explaining why the Red Planet is such a cold, barren place, Jakosky said.

"All the way up through [NASA's] Mariner 6 and 7 in 1969, you could think of the potential for life on Mars as declining," Jakosky said. "In 1971, we orbited the Mariner 9 spacecraft, and that changed things. It took global pictures of Mars, and we saw things that looked very Earth-like, including streambeds, river channels and volcanoes. People thought, 'Well, maybe there's the potential for liquid water and potential for life after all.'"

In the 1970s, the NASA Viking missions landed on Mars and took samples of the soil to look for signs of microbial life. But they recorded none, Jakosky said. In fact, the Viking mission scientists called Mars "self-sterilizing," describing how the combination of the sun's UV rays and the chemical properties of the soil prevented life from forming in those soils, according to NASA. [Seeing Things on Mars: A History of Martian Illusions]

Spacecraft in the 1990s renewed the search for water. The Mars Global Surveyor orbited the planet and took high-resolution images of the surface, finding evidence of ancient gullies. Additional watery evidence came from Martian meteorites that have smashed into Earth, carrying telltale signs of liquid flowing through them, Jakosky said.

Since then, robotic missions have scoured the Red Planet for signs of liquid water. Frozen water is locked up in Mars' roughly mile-thick (1.6 kilometers) ice caps, and enough water vapor resides in the atmosphere to form clouds. Even so, liquid water is more elusive, Zurek said.

Perhaps Mars had water millions or billions of years ago, but that water has since frozen on the surface or been lost to space, Zurek said. (The NASA spacecraft Maven is already examining the Martian atmosphere and helping scientists decipher how Mars lost its water, if that did happen, he said.)

The new finding gives researchers a good spot to look for life on Mars, Zurek said. But the newfound salty streaks aren't like rivers that flow on Earth, he cautioned. [5 Mars Myths and Misconceptions]

"If I pour pure liquid water out on the [Martian] surface today, it's either going to boil way into the atmosphere or it's going to freeze there on the surface," he said.

Any water on Mars is likely laden with salts called perchlorates, which lower water's freezing point to about minus 70 degrees Celsius (minus 94 degrees Fahrenheit), Zurek said.

Moreover, the liquid water — if indeed it is that — only appears during the warm seasons, he said.

"These features grow in a slow, seasonal kind of way, not in a rapid outburst of a flow or a stream," Zurek said. "But nevertheless, here's a source of water that could be staying liquid for a time on the planet."

Extremely salty water isn't necessarily good for life, but perhaps extremophiles can live in those environments, he said.

"We don't know what the evolution of life might have been on the planet, if it ever originated," Zurek said. "But at least this tells us some places where we could go look for evidence of this. It is briny, and there may not be much of it, but it is a place that we could go look."

In a way, the discovery isn't so different from what astronomers were looking for years ago, he said.

"It's not that ancient canal network delivering massive amounts of water out to the desert, but it's curious the way that those early themes over 100 years ago are still playing today," Zurek said.

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V. New Calendar Problems After the Exile.

The Jews and the Babylonian Calendar.-When the Jews returned to Palestine after the Babylonian exile, they brought with them the Babylonian month names in modified form. For example, Abib became Nisan, from Nisanu, the first month of the Babylonian year. Some authorities think that until after the Exile the Hebrews did not insert a second Adar&mdasha 13th month&mdashto correct the calendar. But the Passover had to be synchronized with the barley harvest therefore the Jews, from earliest times, must have had a 13th month or its equivalent. It is clear that the Israelites were not faithful in observing the Levitical law, but there is no reason to suppose that they never observed the Passover throughout the centuries.

Some think that the returning Hebrew exiles adopted the Babylonian calendar outright, including their 19-year cycle, and their exact system of inserting extra months. There is documentary evidence that the Jews after the captivity used the equivalent of the 19-year cycle, that is, the insertion of 7 extra months in 19 years, but there is no proof that they adopted the Babylonian custom of inserting a second Elul (the 6th month) at times instead of a second Adar. Jewish authorities have always held that only the second Adar was used, and other authorities agree that in this they differed from the Babylonians. The reason for this was probably the fact that doubling the 6th month, Elul, instead of the 12th, Adar, would introduce an irregular interval between the spring and fall festivals, and thus cause confusion in attending the autumn feasts.

The Bible gives no direct evidence on the question, but the command to keep the Passover in the 1st month, the &ldquomonth of ears,&rdquo and to observe three feasts in the 7th month, strongly implies that the autumn feasts were intended to come 6 months after the month of ears, and therefore that there was no irregularity in the interval from Nisan through Tishri.

In fact, a second Elul would have no significance in the Hebrew calendar, for the necessity for inserting the 13th month arose only from the requirement of keeping Nisan in line with the barley harvest. This could best be accomplished by adding a second Adar, just preceding Nisan. Placing the extra month 6 months earlier&mdashif indeed the need for it could be predicted that far ahead&mdashwould have been of no advantage, and would have involved the disadvantage of interrupting the normal sequence of the festival months.

The Nineteen-Year Cycle.&mdashThe adoption of a 19-year cycle would have been very helpful in fixing in advance the time of the Passover. As long as the insertion of the 13th month could not be announced until the barley crop was examined in Adar, the month of the Passover could not always be known far enough ahead to avoid inconvenience to those who had to make their plans to attend. But a 19-year cycle would have enabled them to space 7 extra months in every 19 years in a regular sequence of 2-year and 3-year intervals, and to keep the Passover date within the known season of ripening barley. The calendar would be regulated systematically and the 13-month years, recurring at predetermined intervals in each cycle, would always be known in advance.

This 19-year cycle can be explained as an expression of the relationship between solar and lunar years namely, that 235 lunar months almost exactly (within an hour or two) equal 19 solar years. But 19 lunar years of 12 months each would total not 235 but 228 months therefore if an extra lunar month is inserted 7 times in every 19 years, the 19th lunar and solar years will end together. If, for example, the spring equinox fell on Nisan 1 in any given year, it would come on Nisan 1 again 19 years later.

The Babylonians developed such a cycle experimentally. By the early 4th century B.C. they inserted the extra month always in the same years of each 19-year cycle: a second Addaru (Adar) in what we call the 3rd, 6th, 8th, 11th, 14th, and 19th years, and a second Ululu (Elul) in the 17th. (It is known which years had 13 months but not which years the Babylonians called the &ldquoyear 1&rdquo of each cycle hence these numerals are arbitrary.) The Jews, however, seem never to have employed a second Elul, but only the second Adar. The question of when the Jews adopted the 19-year cycle is not settled. Since that cycle was known in Babylonia along before the Christian Era, and many Jews lived there from the 6th century B.C., it would seem hardly probable that the Jewish rabbis who were in charge of the calendar would remain ignorant of the principles of calendrical calculation until the fixed calendar was introduced, long after Christ&rsquos day. It is probable that such principles were known long before the traditional methods were abandoned. Up to the time of the destruction of the Temple, the barley harvest was the major factor, but after that, and especially after the Jews were driven away from Jerusalem, it was less relevant to the problem that the convenience of uniform calculation in widely scattered areas.

Although the Bible nowhere hints of any 19-year cycle, the barley harvest rule would automatically result in an average of 7 extra months in every 19 years. Thus the laws of the festivals, without specifying any calendrical rules as such, served to regulate the Palestinian calendar naturally and simply.

Calculation of the Months Versus Observation.&mdashThe question of the 13th month arose only once in two or three years, but the question of the beginning of the month was ever present. Especially after the captivity, when the majority of Jews remained in Babylonia, it was a very real problem to keep all the faithful observing the new moons and festivals together. The mere difference in the dating of documents was a minor matter, but the prospect of some Jews profaning sacred days while others were observing them was abhorrent to the pious.

The sanctity of the Temple and the prestige of the priesthood kept the Babylonian Jews looking toward Palestine for authority in this matter. Thus the postexilic calendar, even as followed by those Jews who remained for centuries in Babylonia, was regulated in Jerusalem. The first day of the month&mdashat least after each 29-day month&mdashwas announced by fire signals repeated from mountaintop to mountaintop to the outlying districts of Palestine, and even on to Babylonia. Eventually, however, false beacons, lighted a day early by the Samaritans, misled the distant Jews into beginning a new month after 29 days when the outgoing month should have had 30 days. Consequently the fire signals were replaced by messages sent by runners.

In Egypt, where fire signals could not be used, and afterward in all countries outside Palestine, the Jews came to observe new moons and festivals on two successive days, in order to be sure of having the right day. Even a month that followed a 29-day month could not be assumed to have 30 days this doubt as to the first of the new month led to the observance of both the 30th and the day following. This custom was well known in Rome. Horace referred in his Satires (i. 9. 67-70) to the Jewish &ldquotricesima sabbata,&rdquo or &ldquo30th-day sabbath&rdquo:

&ldquoHorace: ‛Certainly I do not know why you wish to speak secretly with me, you were saying.&rsquo

&ldquoFuscus: ‛I remember well, but in a better time let me speak: today is tricesima

sabbata: do you wish to offend the circumcised Jews?&rsquo&rdquo

After the lengths of the months became a matter of calculation, they could be known in advance without depending on direct observation. Unfortunately we do not know when the change was made from observation to a regular sequence of 30-day and 29-day months. We have considerable direct evidence of postexilic calendar practice from dated Jewish documents found in Egypt, but the evidence from these sources has given rise to differences of opinion on the question of calculation versus observation.

It is likely that the calendar officials employed methods of calculation while still retaining the practice of summoning witnesses to report the appearance of the crescent every month, or at least for the month of Nisan. Such traditional procedures would naturally be retained long after they had become unnecessary.

During the period when the month depended on the observation of the crescent, or on confirmation by witnesses, there was uncertainty in distant places as to the correct day of the month, for, on account of certain variable factors, the actual appearance of the crescent could not be predicted. The failure to see a crescent on the evening after the 29th of the month might mean that the month should have 30 days, but it might also mean that atmospheric conditions unfavorable to visibility might delay its being seen in some places later than in Jerusalem. And the difference in longitude between Palestine and Babylonia could sometimes mean that the crescent became visible in Jerusalem after it had already set for Babylonia (see next section). These elements of uncertainty operated even after the astronomical new moon, called &ldquothe moon in conjunction,&rdquo could be computed.

The Moon and the Observed Lunar Month.&mdashThe interval between the astronomical new moon and the visible new moon (or crescent), with which the ancient Semites began each month of their observed lunar calendar, is variable. As the earth moves in one year round the sun, the moon circles the earth 12 times and a fraction. During each revolution of the moon (which marks a lunar month), that body passes between the earth and the sun, and also passes the point on the opposite side of the earth from the sun. When we see it opposite the sun, with its face completely illuminated by sunlight, we say that the moon is &ldquofull.&rdquo When it passes between us and the sun, we do not see it at all because the side toward us is unlighted. When it emerges from between the earth and the sun and becomes visible to us in crescent form&mdashthat is, we see the edge of its lighted portion&mdashwe say that it is &ldquonew.&rdquo

In order to understand this better, let us visualize an imaginary line connecting the center of the earth and the center of the sun. As the moon circles our globe its path lies in a variable plane tilted at an angle in relation to that of the earth therefore it is sometimes above and sometimes below the plane of the earth&rsquos orbit as each month it passes between us and the sun and crosses the earth-sun line. If, as happens occasionally, the moon intersects this line, so that its shadow falls directly on our globe, observers within that shadow see its black disk darkening part or all of the sun in a solar eclipse. Most of the time, when it crosses above or below the imaginary line, it does not obscure the sun, but remains invisible, and therefore the exact time of the crossing (which astronomers call conjunction) cannot be observed. The time of conjunction (the astronomical new moon) is given in almanacs and on some calendars, where it is symbolized by a solid black disk.

But it is not often that the crescent becomes visible in the evening sky on the day marked &ldquoNew Moon&rdquo in the almanac. When the moon passes conjunction during the day, it is too nearly in line with the sun to be seen that evening after sunset. Only after an interval&mdashaveraging about a day and a half&mdashdoes it move far enough past the sun to bring its lighted side toward the earth sufficiently to appear as a crescent. When the crescent becomes visible, it may be seen on one part of the earth just after sunset, but observers on other parts of the globe farther east, for whom the moon will have already set, cannot see the crescent until the next evening. That is why the lunar month, starting with the observation of the crescent, could sometimes begin a day earlier in Egypt or Jerusalem, for example, than it would in Babylon.

The interval between conjunction and the visible crescent varies not only with the hour of conjunction and the locality, but also with the speed and angle of the moon&rsquos course, which are variable. When it is slower, the moon takes longer&mdashperhaps two or three days&mdashto move far enough from the sun to be seen. Further, atmospheric conditions affect visibility, and in certain seasons the crescent may be entirely obscured by clouds on the first evening, and so a 29-day lunar month might be given 30 days and the new month delayed one day.

The Postexilic Month Names.&mdashAfter the return from Exile, the Babylonian month names were adopted, in slightly changed spelling, as has been mentioned. As for the beginning of the year, both fall and spring reckoning seem to be used in the postexilic books of the Bible. It is to be kept in mind that regardless of whether the year is reckoned from the autumn or from the spring, Nisan is always numbered as the 1st month, Tishri the 7th, and Adar the 12th. Thus the civil year begins with the 7th month and ends with the 6th. This alignment of the months, and the approximate equivalents in our calendar, is made clear by the following tabulation:

THE JEWISH CALENDAR

(With postexilic month names derived from Babylonia)

Religious Year(Spring to Spring)

Beginning of Jewish months(varying with moon, within range of one month)

Civil Year (Fall to Fall)

* Month names not mentioned in the Bible.
&dagger In leap years a second Adar follows Adar, preceding Nisan.

The Postexilic Year in the Bible.&mdashEzekiel does not make it clear whether the years of his era, beginning with the exile of Jehoiachin, were reckoned from Nisan or from Tishri, or were counted by anniversaries from the date of the king&rsquos captivity. But if Ezekiel, as is generally held, reckoned the year from the spring, he may have done so because he lived in Babylonia and used the official Babylonian calendar, which began the year with Nisanu (Nisan). Thus his usage would have no bearing on Jewish calendar practice. Haggai, and presumably his contemporary and colleague, Zechariah (although the latter is inconclusive), are generally believed to have used the spring year, for if the events of Haggai 1:1 and 2:1, 10 are related in chronological order, the 7th and 9th months followed the 6th month in the 2nd year of Darius, as could not have occurred if the 7th month had begun a new year. The book of Esther, which identifies Nisan as the 1st month, Sivan as the 3rd, and Adar as the 12th, sheds no light on how the Jews reckoned the beginning of the year, since the dates in this book are given in connection with official acts of leaders in the Persian government. These events would presumably be dated in the Babylonian calendar, which the Persian rulers adopted from the time that Cyrus conquered Babylonia.

In the time of Ezra and Nehemiah (Ezra-Nehemiah was originally one book), there is proof that the returned Jews counted the years of the king from the fall, presumably by the civil year beginning with Tishri. Nehemiah mentions Chisleu (Kislev, the 9th month) as preceding Nisan (the 1st month) in the 20th year of Artaxerxes (Nehemiah 1:1 2:1). Evidently he was thinking in terms of the old regnal year of Judah and reckoning from the 7th month, Tishri, rather than the Persian new year in Nisan. Although the events mentioned in these two months occurred in the Persian king&rsquos palace, the book was not written until after Nehemiah had gone to Jerusalem and engaged in the rebuilding of the Jewish community there. In such a situation&mdashunder the restoration of a Jewish administration at the ancient capital of Judah&mdashit was natural that there should be a resurgence of patriotism, and a return to the old calendar and regnal year of Judah. Further, a document from a Jewish colony in Egypt, written in the same century with Ezra and Nehemiah, shows that these Jews in Egypt also used a Jewish calendar year beginning in the fall.


What is it like to live on Mars time? One family finds out.

The family of David Oh, a flight director for NASA's Curiosity Mars rover mission, opted to join him in synching their lives to the Martian day, which is about 40 minutes longer than the Earth day.

David Oh’s eldest son taped aluminum foil over his windows. His daughter painted a sign warning visitors away from the front door. His wife pulled the phone cord out of the wall and turned the couple’s cellphones off.

David’s time on Earth had come to a temporary end — and he was taking his family with him.

As soon as the rover Curiosity dropped onto the Martian surface on Aug. 5, David and hundreds of his fellow scientists and engineers at NASA’s Jet Propulsion Laboratory switched from Earth time to Mars time.

As the lead flight director for the Mars Science Laboratory team, David would sync his life up with the rover’s for the first 90 Martian days of the Curiosity mission. It may not be rocket science, but it’s quite an undertaking.

A Mars day, called a sol, is 39 minutes and 35 seconds longer than a 24-hour day on Earth. That small difference adds up fast, so that noon becomes midnight after 21/2 weeks. As scientists wind up sleeping during the day and working through the night, their lives pull away from those of their families.

As Kamala Harris’ portfolio grows, so does the scrutiny

Not the Oh clan. For the first month, all five stuck together, an idea championed by David’s wife, Bryn.

“This project for six years has been so much a part of his life,” she said at the family’s tidy two-story home in La Canada Flintridge. “This was a way that I thought that we could be a part of it.”

The family has learned a lot about Southern California since their experiment began, talking to friendly folk in a Canoga Park bowling alley at 4 a.m. and gawking at late-night partygoers while eating dinner at dawn at Fred 62 in Los Feliz.

They’ve discovered the Hollywood sign isn’t lit at night and that the sand on Santa Monica’s moonlit shores is still the perfect temperature for walking barefoot. They’ve noticed that freeway traffic bottoms out at 3 a.m., then starts to pick up again just an hour later.

During one of their frequent late-night walks in the hills near their house, one of the kids saw two shooting stars streak across the quiet sky during the Perseid meteor shower.

The idea of working on Mars time goes back to the 1997 Pathfinder mission, which sent the first rover to the Red Planet.

The beetle-like Sojourner rover was designed to skitter around the surface for a week, sending back data once a sol. Members of the Pathfinder team wanted to analyze the results as quickly as possible so they could plan the rover’s next moves. To minimize delays, they decided to work on Mars time too.

Sojourner kept going all week, then continued for a second and a third. The Earthlings did their best to keep up, but after a month they’d had enough.

“The team rebelled,” said Andrew Mishkin, a senior systems engineer on that mission who has endured three stints on Marstime himself. “They were just too exhausted to continue.”

Living on Mars time is like moving two time zones to the west every three days, causing scientists and engineers to feel constantly jet-lagged. That throws off the body’s internal clock, which is synced to a 24-hour day and reset by light and dark.

When that system is out of whack for several weeks, negative effects ripple throughout the body.

At first, JPL had no formal policies to keep scientists and engineers from working themselves to the edge of their physical limits. They often logged 18 hours a day, and many tried to stick with Earth time when they were off duty, leaving them utterly drained, Mishkin said.

After the Pathfinder mission ended, JPL asked a panel of sleep experts for advice. The key, the experts said, was to keep the body clock on track so that people could sleep during their “night” and stay alert during their “day.”

To do that, the panel recommended that workers stay on Mars time instead of confusing their bodies by toggling between days and sols. They also suggested setting time limits for shifts, limiting caffeine to small doses, and filling the operations rooms with bright light to suppress levels of melatonin, the sleep-inducing hormone, said Dr. Charles Czeisler, a sleep medicine expert from Harvard University who served on the panel.

Not all of the recommendations were adopted. No “solarium” was built to help the engineers adjust, nor was bus transport arranged to and from JPL to keep sleepy workers from getting behind the wheel. But the lab did install blackout curtains to block sunlight in the middle of the Martian night and provide cots for sleepy scientists and engineers whose bodies were having a hard time adjusting to the switch.

When veterans of previous Mars rover missions first heard of the Oh family’s plans, they didn’t hesitate to tell David and Bryn they were nuts.

For workers with children, the logistics of living on Mars time are particularly complex: school car pools, sports practice, music lessons and other activities must be accommodated. But that didn’t stop the Ohs.

“I want my kids to have the experience of what it’s like to work on the Mars program,” David said. “Even the youngest understands Dad has a cool job, so for me to kind of disappear on them would be a pity.”

Bryn, like her husband, is an MIT-trained engineer. She’s logged the family’s meals, medical appointments, work shifts and bedtimes on a spreadsheet. She even took a month off from her job as a software training consultant to manage the elaborate Mars-time experiment.

To keep the kids awake when Mars days are Earth nights, she planned a 10 p.m. backyard barbecue, a midnight picnic in Santa Monica and a 3 a.m. run for Krispy Kreme doughnuts.

The first few days seemed charmed. David came home around midnight to a brightly lit house with a cake baking in the kitchen. The kids yelled their greetings when he opened the door.

But a week after the Mars landing, the family started to drag. The kids — 8-year-old Devyn, 10-year-old Ashlyn and 13-year-old Braden — struggled to stay awake until sunrise, when it was finally bedtime on Mars.

Their schedules became so misaligned that the family stopped marking their days by Earth time. Instead, they used words like “yestersol” and “solmorrow.”

Even David, whose work and home life are both pegged to the Red Planet, experienced a disconcerting moment when he collected Devyn from a play date around 5 p.m. and asked the friend’s mom if the kids had eaten lunch yet.

“She was looking at me like, ‘Are you crazy?’ ” David said.

The time-traveling adventure kept the family together, but Bryn said she missed feeling connected with the world outside the Mars bubble.

“There’s just an amount of contact you get by being on the road, going grocery shopping, whatever it is,” she said. “I’m a little bit jealous that (David) gets to go into work in the middle of the night and be with people.”

For Bryn and the kids, the hardest part is now over. School started last week — just as Mars time had cycled around to nearly coincide with the East Coast time zone — so most of the family is transitioning back to their earthly routines.

“It really felt like we were on vacation, like we really had gone to another place,” Bryn said. “Seeing Los Angeles in a completely different light — we’re going to miss that.”

The vacation is almost over. Bryn has been watching their time zone edge ever closer to California. Last Tuesday, they were lined up with Rio de Janeiro on Wednesday, New York. On Saturday, they returned to Pacific Daylight Time.

Get the Monitor Stories you care about delivered to your inbox.

“Will miss Orion in the AM,” she wrote on Twitter. “Will miss looking forward to the dawn.”


4 Answers 4

While the book uses the term, it does not explain the definition or exact length.

Mars Solar Days and 24-hr Clock Convention

Following the long-standing practice originally adopted in 1976 by the Viking Lander missions, the daily variation of Mars solar time is reckoned in terms of a "24-hour" clock, representing a 24-part division of the planet's solar day, along with the traditional sexagesimal subdivisions of 60 minutes and 60 seconds. A Mars solar day has a mean period of 24 hours 39 minutes 35.244 seconds, and is customarily referred to as a "sol" in order to distinguish this from the roughly 3% shorter solar day on Earth. The Mars sidereal day, as measured with respect to the fixed stars, is 24h 37m 22.663s, as compared with 23h 56m 04.0905s for Earth.


Mars mission scientist will live a 25-hour day

Squyres is preparing to live on Mars time for the duration of the two-rover mission, expected to be at least four months. Spirit is scheduled to touch down in the red planet's Gusev Crater on Jan. 3 at 11:35 p.m. EST its twin, Opportunity, will land at Meridiani Planum on Jan. 25 at 12:05 a.m. EST.

The Jet Propulsion Laboratory (JPL) in Pasadena, a division of the California Institute of Technology, manages the Mars Exploration Rover project for NASA's Office of Space Science, Washington, D.C. Cornell University, Ithaca, N.Y., is managing the science suite of instruments carried by the two rovers.

"Our vehicles are tied to the Martian day/night cycle," says Squyres, who is professor of astronomy at Cornell. "They rely on a vision system to avoid obstacles," and being solar powered they must operate during daylight and "sleep" at night.

Because the rovers' daily communications windows also are tied to this cycle, Squyres, along with more than 200 other scientists and engineers, must lengthen his days to stay in sync.

Squyres admits that the longer days, at first, seem attractive -- "you get to sleep in 39 minutes later every day" -- but points out that there is "very little hard data on the physiological impact of extended Mars-time living."

The fundamental problem, says Squyres, is that team members must keep a longer day while exposed to outside stimuli that run on an exact 24-hour cycle.The entire rover team will work at the mission control center at JPL. They already have rented apartments in a quiet neighborhood equipped with light-tight blackout shades, and some of them will wear specially made Mars watches that record an additional 39 minutes, 35 seconds every day. But when rover team members step outside, they will be bombarded with external stimuli running on the 24-hour clock to which their bodies are accustomed.

"We decided we needed to get some serious advice in this area," says Squyres. When, jet-lagged and exhausted, he ran into Cornell sleep researcher James Maas at Pittsburgh airport in 2000, both realized that a collaboration would be a boon for data-hungry sleep researchers and for the rover team.

"While we were doing our own experiments, there was the opportunity for us to be the subject of someone else's experiment," says Squyres.

Consequently about 40 members of the rover team will be the subjects of the sleep study. Small wristwatch-like accelerometers will keep a record of the scientists' motion through the days and nights of the Mars mission. From the accelerometer readings, the sleep-research team will deduce when the scientists were awake and when they were asleep.

Workshops with sleep experts from Harvard, Brown, Stanford and the NASA Ames research center also have helped shape the Mars team's strategies.

"The key is not to overschedule people," says Squyres. Scientists will stick to a six-sol workweek, working four sols and taking a two-sol weekend.

But engineers on the team with permanent homes in Pasadena will get a longer, three-sol weekend. The engineers "have groceries to buy, lawns to mow, PTA meetings to go to," and must contend with more signals from the 24-hour world than the visiting scientists, says Squyres.

He is most worried, though, about the "wicked case of Martian jet lag" he will get when Opportunity lands Jan. 25. The rover's landing site is almost 180 degrees away from Spirit's, meaning that when Squyres leaves the Spirit team to join the Opportunity group, he will be about 12 hours off schedule. It is the Martian equivalent of a trip from New York to Australia -- without the benefit of a daylong plane ride during which to adjust.

There is one vestige of Earth time Squyres won't be able to escape, though: the press conference. So if, come January, Squyres looks a bit bleary-eyed in front of the cameras, remember that it might just be 2:30 a.m. back in Gusev Crater.

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.


How did Mars come to have a 24 hour 39 minute day? - Astronomy

> It is currently not possible to use ssh to login between systems on MCT and any earth time zone

Full handshake requires a few hours of round trips.

6 trips x 11 min each: That is 66min for the handshake.

Disclaimer: Mostly just posting this to plug Escape Pod. No affiliation, but it’s one of my favorite short fiction podcasts.

Then you start to get the new factor of planetary distance wobble adjustments. Which will be fun as you start to add https:/˾n.wikipedia.org/wiki/Three-body_problem into time models.

or boot the thing from a dban ISO and wipe the SSD, re-use it.

Judging from our past several decades of network effects, Iɽ guess earth-origin operating systems will still dominate, with perhaps a long tail of poorly-adopted alternatives (as with, on the language side, BELTABOL: https:/˽rive.google.com˿ile˽˱zTGjy9KeW4cqagXHlVDwKmcZ1mE. ).

If we were to build a colony on Mars with normal people doing normal everyday things, we need something more than that. The first question we want to ask ourselves is, do we want to keep the SI defined second? If we don't care, then we have free reign to do whatever we want. We can define a Mars second to be 1⾆,400th of a Mars day, and keep the 24 hour, 60 minute, 60 second time system we use on Earth. Or we switch to a metric time system, with a 10 hour day, 100 minute hours, 100 second minutes. Or a 1 day long day, and deci, ceni, milli, micro days. Or whatever.

If we want to keep SI compatibility, we need to keep the second. The Martian solar day is 87,755.224 seconds long. 87,755 factors into 5^2 * 53 * 67. So we can do 25 hours per day, 53 minutes per hour, 67 seconds per minute to give an 87,755 second day. Unfortunately there would need to be a leap second once every 4-5 days.

Then there's the question of the calendar. Perhaps fortunately, this gives us the opportunity to restart from scratch, because the calendar we use is such a goddamned clusterfuck, even worse than our time system. Unfortunately, the number of days in a Martian year (668 and change) does not lend itself to a clean division into tidy periods. You could have 23 months of 29 days each, with each month having 4 7 day weeks plus one holiday. This will give you a 667 day year. Add another annual holiday at the beginning of the year, plus an optional leap-holiday in the middle of the year.

Or you could split it up into 37 months of 3 weeks, each with 6 days. This gives you a 666 day year, so sprinkle in 2-3 bonus holidays per year.

There are a lot of considerations. It needs to be given more thought. Hopefully more thought than we've given to Earth's timekeeping systems.

I think absolutely yes. Any Mars colony is going to import a lot of equipment and technology from Earth. All of that is going to assume the SI second. Not just for measuring time, but also as part of the definition of derived units such as newtons. Martian colonists will have no practical choice but to use the SI second since all their Earth-manufactured equipment is going to assume it.

Plus, if they tried to introduce a distinct Martian second, soon theyɽ have a mix of SI units (based on the SI second) and slightly different Martian units (based on the Martian second), and that would produce Mars Climate Orbiter style disasters.

> Perhaps fortunately, this gives us the opportunity to restart from scratch

People won't. People will want to use the Earth calendar because they are keeping in sync with Earth news and Earth culture. Maybe after a few centuries, Mars will feel sufficiently independent from Earth, that it might want to introduce a new calendar. However, by then Martians will be thoroughly used to the Earth calendar, it will be a centuries-old part of their Martian culture heritage, and they probably won't want to change it.

I like Kim Stanley Robinson's approach, as described in the Mars trilogy. They use standard seconds, but at 12:00 midnight, the clocks just stop for about 39 minutes. (Computers just use seconds-since-the-epoch or something and are unaffected.)

Martian colonies will still care about Earth calendars, but only to the extent that they have to deal with Earth. Kind of like dealing with a different timezone on Earth.

How important are the seasons going to be for people who have to spend the vast majority of their time indoors due to the lack of a breathable atmosphere – and possibly even underground for protection against radiation?

Maybe one day Mars will be terraformed and given a breathable atmosphere, and maybe even some kind of artificial magnetosphere can be created to protect against radiation. But that is going to take many centuries.

The fact is that modern societies don't really need a calendar synchronised to the seasons. Most jobs nowadays the seasons are not very important. This is especially true in parts of the world where the difference in weather between the seasons is less marked (like where I live, here it never snows in winter). Fields such as agriculture where seasons are important can always keep track of the seasons independently from the calendar, or using a special purpose agricultural calendar. In fact, that's what is traditionally done in much of the Islamic world – the Islamic calendar was used for most purposes, which is out of sync with the seasons. Those jobs for which seasons were important, such as farmers, also used a separate solar calendar. It was only in the 20th century that the need to participate in the global economy created pressure to use the Gregorian calendar instead.

> I like Kim Stanley Robinson's approach, as described in the Mars trilogy. They use standard seconds, but at 12:00 midnight, the clocks just stop for about 39 minutes

I don't know why youɽ do that. On earth, clocks run from 00:00:00 to 23:59:59 each day. On Mars, youɽ just make them run to 24:39:34 instead. That way you can actually get precise times for events that occur in those extra 39 minutes and 35 seconds that happen each day. (Also, Iɽ hope people on Mars would be using 24 hour time–I'm one of those people who changes all their clocks to 24 hour time on Earth)

> Martian colonies will still care about Earth calendars, but only to the extent that they have to deal with Earth

For the first few decades at the very least, Martian colonies will be dealing with Earth an awful lot. A lot of goods will have to be imported from Earth. There will be a lot of focus on what they can locally manufacture on Mars, but they'll start with basic stuff like foodstuffs and simpler manufactured goods, and it will be a long time before Mars has leading-edge semiconductor fabs or a lot of other stuff like that.

There will also be continual immigration from Earth, and also people returning to Earth (whether temporarily or permanently). That's going to psychologically link them with Earth.

Martians are also going to consume a huge amount of cultural imports from Earth. You think on Mars they won't have Netflix, YouTube, etc? They'll replicate the content library into a Mars-based CDN and people will be watching it on Mars. It is going to take a long time before natively produced Martian media˾ntertainment content becomes more popular than the Earth-imported stuff. And I think that's going to tie Martians to Earth at least as much as trade ties and movement of people back and forth will. Martian colonies will undoubtedly develop some unique cultural aspects, but a huge amount of their culture is just going to be Earth imports.

Quite important, actually. Day and night cycles determine when solar power is available. You'll probably have some outdoor activity by humans (mining, construction, maintenance, etc. ) that would be affected by daylight. (Perhaps most work will actually be done at night to avoid radiation from the sun?) And even in a hardened habitat you might have skylights (maybe long tubes or solar collectors connected to fiber optic cables rather than big windows in the ceiling).

> The fact is that modern societies don't really need a calendar synchronised to the seasons. Most jobs nowadays the seasons are not very important.

I work an indoor job, but still the seasons affect me quite a lot. (It's cold and rainy in the winter.) I don't know what the seasons are like on Mars, but I could imagine outdoor seasonal differences in temperature and light levels could have some impact on colony logistics.

> For the first few decades at the very least, Martian colonies will be dealing with Earth an awful lot.

Sure, but if the lead time between ordering a part and receiving delivery is something like six months or a year, it's probably hard to care that much about what's going on on Earth in real time. Sort of like someone who runs a business that buys parts from vendors in China is probably aware of the Chinese New Year. But that doesn't mean they run their life primarily off of the traditional Chinese calendar.

> I don't know why youɽ do that. On earth, clocks run from 00:00:00 to 23:59:59 each day. On Mars, youɽ just make them run to 24:39:34 instead.

Well, sure, that's the practical solution. But it's less poetic than having some interval every day where the accounting of time is put on hold.

The question is whether that's important enough to justify using as the primary calendar for everyday use. You can always have a "Mars seasons" app which displays current and future Mars seasonal information in terms of the Earth calendar, or in terms of some kind of hybrid Earth-Mars calendar (like my suggestion of using Mars sols but Earth years.)

I don't know what theyɽ do about months. I reckon the easiest thing to do them would be just not to use them, and use a week count instead. A lot of businesses on earth prefer to use week counts instead of months for planning anyway, so we already know that approach works. For medium-term planning, you can divide the sol-weeks of the Earth year into four quarters. (The Earth-year contains 50-51 sol-weeks, so that divides into quarters of 12-13 sol-weeks–some quarters would be 7 sols longer than others.)

Assuming the energy on a Martian colony would come from solar panels, a Martian colony would still need to care significantly about the seasons and time of day.

Sure, in most if not all of the places future humans may come to inhabit, the celestial bodies will obviously have a strong influence on their lives and so they'll have to care. But, as I see it, this is more like marking events in a tool-tracked independent time system instead of having the time system devised around what's happening with celestial bodies around them because they can't do any better.

About the only practical benefit of a Martian colony is to serve as a last-ditch backup of human civilization in the event of an asteroid strike. Mars won't be a powerhouse of industry, commerce, or culture at best there will be some modest scientific output. It's a tomb world.

Give humanity a few millennia to build a Dyson sphere around the sun and maybe then you could start reasonably terraforming Mars into somewhere intrinsically nice to live, over the course of a few additional tens of millennia.

I wouldn't go that far. Yeah, the habitability sucks, but it does have plenty of natural resources. Combined with the low gravity, I suspect it could be a useful manufacturing and refueling hub, especially as a pit stop on the way to the outer planets.

That said, I think Ceres is a bit more viable for that, due to closer proximity to the asteroid belt (since it's in the asteroid belt) and due to it being a giant ball of water ice and hydrocarbons (water and hydrocarbons being pretty crucial for both refueling operations and human colonization). If the gravity on Ceres ends up being too low for human comfort, that just makes it easier to build centrifuge habitats, be it on the surface or in orbit.

I don't think you need a dyson sphere level of energy output, or even a single millennium to terraform mars to be human habitable.

It's a big project, to be sure, but if we were dedicated to it I think we could accomplish it in <1,000 years.

Almost all Martian settlers will be living underground, and even aboveground the light at mid-day is extremely dim. You can set the day to whatever length you want, regardless of the Martian sol, and nobody will notice.

Likewise, months and years on Earth are for tracking agricultural seasons, but nobody will be growing crops on the Martian surface. Set the year to whatever you want, with or without months, and no civilians will notice.

Direct normal insolation on Mars seems to be in the 590 W/m^2 range.

That's brighter than an average winter day in Seattle.

(click on "Month graphs", and then "Maximum".

Even still, being able to see the Martian sky means being exposed to radiation for which no intervening atmosphere or magnetosphere exists to protect you. I don't think this changes much about a Martian settler's unlikeliness to prefer to set their clocks according to solar time.