Astronomy

Where have all the Vulcanoids gone?

Where have all the Vulcanoids gone?


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This answer to Does anything orbit the Sun faster than Mercury? explains that while Vulcanoid asteroids may have been plentiful in the past, large ones have currently been ruled out though smaller ones less than about 6 km might still be there. It's difficult to observe them because from Earth it requires pointing close to the Sun, and from spacecraft that are much closer (i.e. Mercury and lower) it's really hot and difficult to do.

I think that the current limits are set by analysis of historical STEREO images, space telescopes in orbit at 1 AU designed to look at and around the Sun. A Search for Vulcanoids with the STEREO Heliospheric Imager

My understanding is that during solar system formation there were asteroids all over the place as things formed and then collided, but as some bodies became large large swaths were swept clean and some bands remained.

Have any theories been put forth explaining why the vulcanoid belt seems to be depleted of large asteroids? Is this band, while quite stable, simply not stable enough? Do some think that it simply was never populated by large asteroids to begin with for some reason?

Question: Where have all the Vulcanoids gone? (sung to the tune of Where have all the flowers gone?)


The effects of solar radiation are the main suspect for clearing out the vulcanoid region of whatever was there to begin with. Radiation pressure will tend to blow small dust out of the region. Larger objects tend to get cleared out due to the Yarkovsky effect and the YORP effect.

The Yarkovsky effect occurs as a result of temperature variations across a rotating object and the time lag for regions of the object's surface to heat up and cool down as they move into and out of the sunlight. This affects the distribution of the radiated photons (which carry momentum), and over time will act to shift the asteroid's orbit. Vokrouhlický et al. (2000) estimate that this effect would clear kilometre-sized objects out of the vulcanoid region on a timescale of a few billion years.

A further effect that is relevant is the YORP effect (short for Yarkovsky, O'Keefe, Radzievskii and Paddack, see also the question What is the difference between the Yarkovsky effect and YORP effect?). This affects the rotation of irregular objects like asteroids and can result in them spinning up to the point where they break apart. This is thought to be a significant contributor to the population of binary asteroids. In the vulcanoid region, this would be a mechanism for breaking up larger asteroids into fragments small enough for the Yarkovsky effect to rapidly clear them out of the vulcanoid region: Collins (2020) puts this right in the title: "The YORP Effect Can Efficiently Destroy 100 Kilometer Planetesimals At The Inner Edge Of The Solar System".

… The YORP effect destroys Vulcanoids by spinning them up so fast that the gravitational accelerations holding components of the body together are matched by centrifugal accelerations, this causes the body to rotationally fission. i.e break apart. We calculated the timescale of this fission process for a parent Vulcanoid and for each of their subsequent generational fragments. We show that objects with radii up to 100 kilometers in size are efficiently destroyed by the YORP effect doing so in a timescale that is much younger than the age of the Solar System


Vulcanoid

The vulcanoids are a hypothetical population of asteroids that orbit the Sun in a dynamically stable zone inside the orbit of the planet Mercury. They are named after the hypothetical planet Vulcan, which was proposed on the basis of irregularities in Mercury's orbit that were later found to explained by general relativity. So far, no vulcanoids have been discovered, and it is not yet clear whether any exist.

If they do exist, the vulcanoids could easily evade detection because they would be very small and near the bright glare of the Sun. Due to their proximity to the Sun, searches from the ground can only be carried out during twilight or solar eclipses. Any vulcanoids must be between about 100 metres (330 ft) and 6 kilometres (3.7 mi) in diameter and are probably located in nearly circular orbits near the outer edge of the gravitationally stable zone between the Sun and Mercury.

The vulcanoids, should they be found, may provide scientists with material from the first period of planet formation, as well as insights into the conditions prevalent in the early Solar System. Although every other gravitationally stable region in the Solar System has been found to contain objects, non-gravitational forces (such as the Yarkovsky effect) or the influence of a migrating planet in the early stages of the Solar System's development may have depleted this area of any asteroids that may have been there.


In digital reenactments of its early days, the solar system gets rowdy. Near collisions between planets end with Jupiter sending Uranus or Neptune flying in 99 simulations out of 100. Yet both remain. One explanation: A third body took the hit. Calculations hint that a massive, icy planet could have tussled with Jupiter and lost.

Hundreds of specks appear clustered beyond Neptune, a hint that something up to 10 times as massive as Earth might lie beyond. A large planet could supply the necessary gravitational influence to pull them in. New evidence for this celestial body—possibly a rogue world from interstellar space—was unveiled in 2016.


Where have all the Vulcanoids gone? - Astronomy

SwRI Goes Suborbital In Search Of Mercury And The "Vulcanoids"

"Never before in history has it been possible to obtain an ultraviolet spectrum of Mercury," says Stern. "With the data gathered last week, we expect to reveal new details about this mysterious inner planet's surface composition and, hopefully, to help the upcoming NASA MESSENGER mission (pictured above) to Mercury plan its ultraviolet observations."
Boulder - Jan 27, 2004
A new major scientific payload flew in space last week after launching aboard a NASA suborbital Black Brant rocket. The payload, consisting of a telescope/spectrometer combination and an image-intensified imaging system, successfully explored the ultraviolet spectrum of the planet Mercury and also searched for the long-sought belt of small bodies called Vulcanoids that may lie even closer to the Sun than Mercury. Southwest Research Institute (SwRI) provided the payload and is responsible for data analysis.

"The rocket flew a textbook flight and got the goods on our calibration star (Zeta Ophiuchus), Mercury and the Moon -- everything in the flight plan," says Dr. Alan Stern, mission principal investigator and director of the SwRI Space Studies Department. "The secondary payload, the so-called VULCAM (Vulcanoid camera) imager, also worked like a champ, searching for Vulcanoids while the spectrograph studied Mercury itself."

The payload's main instrument is a large (almost 500 pound), highly sensitive, ultraviolet spectrograph designed to observe objects too close to the Sun for the Hubble Space Telescope and other orbital instruments to view. The new SwRI instrument has been dubbed "Big Dog" by its inventors, owing to the large size of the payload.

"We built Big Dog specifically to fill a niche -- exploring objects in the deep inner solar system," explains SwRI's Dr. David Slater, project scientist for the instrument and leader of the field team that took the payload to White Sands for the launch preparations and flight. "This flight proves we can now examine objects -- like Venus, Mercury and bright comets close to the Sun -- that are normally lost in the Sun's glare to orbiting telescopes, on a routine basis. This is a real asset for planetary astronomy and for certain kinds of astrophysics as well."

VULCAM scientist Dr. Dan Durda, also of SwRI, added, "VULCAM is a derivative of an imaging instrument we have flown many times on F-18 aircraft, but which has the potential to become an even more powerful tool for searching for Vulcanoids from 260+ kilometer (165+ mile) altitudes that NASA suborbital missions can reach. VULCAM also performed flawlessly."

"Never before in history has it been possible to obtain an ultraviolet spectrum of Mercury," says Stern. "With the data gathered last week, we expect to reveal new details about this mysterious inner planet's surface composition and, hopefully, to help the upcoming NASA MESSENGER mission to Mercury plan its ultraviolet observations."

Primary funding for this mission came from NASA, with supplemental support from The Planetary Society. The NASA Wallops Island Flight Facility managed the mission and provided both the launch vehicle and the pointing, telemetry and recovery systems required to support the flight. The Center for Astrophysics and Space Astronomy at the University of Colorado at Boulder also collaborated on the mission.

Vulcanoids are a hypothesized population of small asteroids that is exceedingly difficult to observe from the ground because of its proximity to the Sun. Researchers have made previous ground-based searches for Vulcanoids during total solar eclipses, during the brief twilight period after sunset before the Vulcanoids themselves set or just before sunrise after the Vulcanoids have peaked above the horizon.

Messenger Shipped to Goddard for Prelaunch Tests
Greenbelt - Dec 22, 2003
Less than six months from its scheduled launch to Mercury, Messenger is set for the next round of tests to prepare it for the first orbital study of the innermost planet.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.


Contents

Celestial bodies interior to the orbit of Mercury have been hypothesized, and searched for, for centuries. The German astronomer Christoph Scheiner thought he had seen small bodies passing in front of the Sun in 1611, but these were later shown to be sunspots. [1] In the 1850s, Urbain Le Verrier made detailed calculations of Mercury's orbit and found a small discrepancy in the planet's perihelion precession from predicted values. He postulated that the gravitational influence of a small planet or ring of asteroids within the orbit of Mercury would explain the deviation. Shortly afterward, an amateur astronomer named Edmond Lescarbault claimed to have seen Le Verrier's proposed planet transit the Sun. The new planet was quickly named Vulcan but was never seen again, and the anomalous behaviour of Mercury's orbit was explained by Einstein's general theory of relativity in 1915. The vulcanoids take their name from this hypothetical planet. [2] What Lescarbault saw was probably another sunspot. [3]

Vulcanoids, should they exist, would be difficult to detect due to the strong glare of the nearby Sun, [4] and ground-based searches can only be carried out during twilight or during solar eclipses. [5] Several searches during eclipses were conducted in the early 1900s, [6] which did not reveal any vulcanoids, and observations during eclipses remain a common search method. [7] Conventional telescopes cannot be used to search for them because the nearby Sun could damage their optics. [8]

In 1998, astronomers analysed data from the SOHO spacecraft's LASCO instrument, which is a set of three coronagraphs. The data taken between January and May of that year did not show any vulcanoids brighter than magnitude 7. This corresponds to a diameter of about 60 kilometres (37 mi), assuming the asteroids have an albedo similar to that of Mercury. In particular, a large planetoid at a distance of 0.18 AU, predicted by the theory of scale relativity, was ruled out. [9]

Later attempts to detect the vulcanoids involved taking astronomical equipment above the interference of Earth's atmosphere, to heights where the twilight sky is darker and clearer than on the ground. [10] In 2000, planetary scientist Alan Stern performed surveys of the vulcanoid zone using a Lockheed U-2 spy plane. The flights were conducted at a height of 21,300 metres (69,900 ft) during twilight. [11] In 2002, he and Dan Durda performed similar observations on an F-18 fighter jet. They made three flights over the Mojave desert at an altitude of 15,000 metres (49,000 ft) and made observations with the Southwest Universal Imaging System—Airborne (SWUIS-A). [12]

Even at these heights the atmosphere is still present and can interfere with searches for vulcanoids. In 2004, a sub-orbital spaceflight was attempted in order to get a camera above Earth's atmosphere. A Black Brant rocket was launched from White Sands, New Mexico, on January 16, carrying a powerful camera named VulCam, [13] on a ten-minute flight. [4] This flight reached an altitude of 274,000 metres (899,000 ft) [13] and took over 50,000 images. None of the images revealed any vulcanoids, but there were technical problems. [4]

Searches of NASA's two STEREO spacecraft data have failed to detect any vulcanoid asteroids. [14] It is doubtful that there are any vulcanoids larger than 5.7 kilometres (3.5 mi) in diameter. [14]

The MESSENGER space probe took a few images of the outer regions of the vulcanoid zone however, its opportunities were limited because its instruments had to be pointed away from the Sun at all times to avoid damage. [15] [16] Before its demise in 2015, however, the craft failed to produce substantial evidence on vulcanoids.

A vulcanoid is an asteroid in a stable orbit with a semi-major axis less than that of Mercury (i.e. 0.387 AU). [7] [17] This does not include objects like sungrazing comets, which, although they have perihelia inside the orbit of Mercury, have far greater semi-major axes. [7]

The vulcanoids are thought to exist in a gravitationally stable band inside the orbit of Mercury, at distances of 0.06–0.21 AU from the Sun. [18] All other similarly stable regions in the Solar System have been found to contain objects, [8] although non-gravitational forces such as radiation pressure, [9] Poynting–Robertson drag [18] and the Yarkovsky effect [5] may have depleted the vulcanoid area of its original contents. There may be no more than 300–900 vulcanoids larger than 1 kilometre (0.62 mi) in radius remaining, if any. [19] A 2020 study found that the Yarkovsky–O'Keefe–Radzievskii–Paddack effect is strong enough to destroy hypothetical vulcanoids as large as 100 km in radius on timescales far smaller than the age of the solar system would-be vulcanoid asteroids were found to be steadily spun up by the YORP effect until they rotationally fission into smaller bodies, which occurs repeatedly until the debris is small enough to be pushed out of the vulcanoid region by the Yarkovsky effect this would explain why no vulcanoids have been observed. [20] The gravitational stability of the vulcanoid zone is due in part to the fact that there is only one neighbouring planet. In that respect it can be compared to the Kuiper belt. [18] The outer edge of the vulcanoid zone is approximately 0.21 AU from the Sun. Objects more distant than this are unstable due to interactions with Mercury and would be perturbed into Mercury-crossing orbits on timescales of the order of 100 million years. [18] The inner edge is not sharply defined: objects closer than 0.06 AU are particularly susceptible to Poynting–Robertson drag and the Yarkovsky effect, [18] and even out to 0.09 AU vulcanoids would have temperatures of 1,000 K or more, which is hot enough for evaporation of rocks to become the limiting factor in their lifetime. [21]

The maximum possible volume of the vulcanoid zone is very small compared to that of the asteroid belt. [21] Collisions between objects in the vulcanoid zone would be frequent and highly energetic, tending to lead to the destruction of the objects. The most favourable location for vulcanoids is probably in circular orbits near the outer edge of the vulcanoid zone. [22] Vulcanoids are unlikely to have inclinations of more than about 10° to the ecliptic. [7] [18] Mercury trojans, asteroids trapped in Mercury's Lagrange points, are also possible. [23]

Any vulcanoids that exist must be relatively small. Previous searches, particularly from the STEREO spacecraft, rule out asteroids larger than 6 kilometres (3.7 mi) in diameter. [14] The minimum size is about 100 metres (330 ft) [18] particles smaller than 0.2 μm are strongly repulsed by radiation pressure, and objects smaller than 70 m would be drawn into the Sun by Poynting–Robertson drag. [9] Between these upper and lower limits, a population of asteroids between 1 kilometre (0.62 mi) and 6 kilometres (3.7 mi) in diameter is thought to be possible. [10] They would be almost hot enough to glow red hot. [17]

It is thought that the vulcanoids would be very rich in elements with a high melting point, such as iron and nickel. They are unlikely to possess a regolith because such fragmented material heats and cools more rapidly, and is affected more strongly by the Yarkovsky effect, than solid rock. [5] Vulcanoids are probably similar to Mercury in colour and albedo, [7] and may contain material left over from the earliest stages of the Solar System's formation. [12]

There is evidence that Mercury was struck by a large object relatively late in its development, [5] a collision which stripped away much of Mercury's crust and mantle, [16] and explaining the thinness of Mercury's mantle compared to the mantles of the other terrestrial planets. If such an impact occurred, much of the resulting debris might still be orbiting the Sun in the vulcanoid zone. [13]

Vulcanoids, being an entirely new class of celestial bodies, would be interesting in their own right, [23] but discovering whether or not they exist would yield insights into the formation and evolution of the Solar System. If they exist they might contain material left over from the earliest period of planet formation, [12] and help determine the conditions under which the terrestrial planets, particularly Mercury, formed. [23] In particular, if vulcanoids exist or did exist in the past, they would represent an additional population of impactors that have affected no other planet but Mercury, [16] making that planet's surface appear older than it actually is. [23] If vulcanoids are found not to exist, this would place different constraints on planet formation [23] and suggest that other processes have been at work in the inner Solar System, such as planetary migration clearing out the area. [18]


Dark skies and light pollution discussed at astronomy festival in Bryce Canyon National Park

Rangers at Bryce Canyon National Park held presentations at the Sunrise Point Amphitheater Thursday on everything from planets to black holes to birds as part of the park's annual Astronomy Festival. More than 50 people showed up for the evening program, bundled in blankets and coats to combat the high-elevation nighttime cold. (Photo: K. Sophie Will/The Spectrum & Daily News)

Dozens gathered to look up at the stars rather than down to the hoodoos at Bryce Canyon National Park this week with the park’s annual Astronomy Festival.

For more than 50 years, Bryce Canyon has held ranger-led astronomy programs, though the park only gained its International Dark Sky designation in 2019. This year’s celebration is the first astronomy festival held since the designation, as last year’s event was cancelled due to the COVID-19 pandemic.

This year’s festival marks a return to large events after the COVID-19 pandemic for all Utah national parks, though Bryce Canyon has held some events with COVID restrictions through the past year.

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“There’s no place quite like Bryce Canyon by day, and no time like a new moon in June to enjoy it by night,” a press release said.

Day programs included family friendly arts and crafts with opportunities to make sundials and paper constellations, and contribute to an artwork which will be unveiled on Saturday.

However, because of the lasting impacts of the pandemic, this year’s festival did not include the usual telescope tours, model rockets or a keynote speaker at Ebenezer’s Barn and Grill – though they will return in the future.

At twilight, park rangers held presentations at the Sunrise Point Amphitheater exploring space, covering everything from planets to black holes to birds.

Visitors at Bryce Canyon National Park this week celebrated the annual Astronomy Festival with lectures, presentations, board displays and stargazing, among other activities. The park earned an official International Dark Sky designation in 2019 but had already been hosting the festival for more than 50 years. (Photo: K. Sophie Will/The Spectrum & Daily News)

“We want to, for what we are doing here at this park, encourage stewardship of our night skies,” Ranger Ben Taylor said in his evening program entitled “Looking Back at Bryce, Looking Back at Home.”

Over 50 people showed up for the evening program on Thursday, bundled in blankets and coats as June at this elevation reached 50 degrees.

Taylor showed how the night sky looks very different from different planets and the constant stars humans have relied on become more obsolete the further from Earth you travel.

As darkness loomed, Taylor asked participants to take home their appreciation of the stars and become stewards of dark skies as all Utah national parks are.

“The first step in stewardship is knowledge, is learning about things, is getting excited about them,” he said.

Visitors at Bryce Canyon National Park this week celebrated the annual Astronomy Festival with lectures, presentations, board displays and stargazing, among other activities. The park earned an official International Dark Sky designation in 2019 but had already been hosting the festival for more than 50 years. (Photo: K. Sophie Will/The Spectrum & Daily News)

Immediately after, constellation tours were held at Sunset Point, with red string lights guiding the way along the trail toward the lookout.

Rangers reminded visitors that white light ruins human night vision and to only use red light. Attendees were divided into two groups, each with their own star guide, and using a laser light the rangers pointed out famous and not-so-famous constellations.

Rangers at Bryce Canyon National Park held presentations at the Sunrise Point Amphitheater Thursday on everything from planets to black holes to birds as part of the park's annual Astronomy Festival. More than 50 people showed up for the evening program, bundled in blankets and coats to combat the high-elevation nighttime cold. (Photo: K. Sophie Will/The Spectrum & Daily News)

Attendees said tickets for the constellation tours held right after the evening programs were gone by 8 a.m., but some found other non-official ways to stargaze.

Even nearing midnight, cars travelled in and out of lookout points to look up at the heavens.

Jeff Romano, 65, of Chicago, attended Thursday night’s program and said it was nothing like what he could see in the city, or even Zion National Park which just earned its dark sky designation.

“When we were in Zion before, but we didn’t see much more than I saw north of Chicago,” he said. “So here I’m looking forward to seeing more.”

After the constellation tours, visitors kept gendering upwards, marveling at what they can’t get back home.

“You might see a few dozen where we live but here it’s incredible,” Stuart Engel of Las Vegas said.

Rangers at Bryce Canyon National Park held presentations at the Sunrise Point Amphitheater Thursday on everything from planets to black holes to birds as part of the park's annual Astronomy Festival. More than 50 people showed up for the evening program, bundled in blankets and coats to combat the high-elevation nighttime cold. (Photo: K. Sophie Will/The Spectrum & Daily News)

Utah has more dark sky designations than any other singular location in the world, with Zion being the fifth and final Utah national park to receive the honor within the past few weeks.

Kevin Poe, a Bryce Canyon ranger and owner of Dark Ranger Telescope Tours in Bryce Canyon City, said in September that astronomy tours are essential for understanding what’s written in the stars as well as an opportunity to capitalize on tourism.

“It’s something that you can celebrate in person rather than just making a pilgrimage that leads you to an overlook and the beauty of the night sky. Having some telescopes and educated professionals who are good at bringing these kinds of connections to the great big universe alive for individuals, that’s why Utah is the place to come stargaze,” Poe said.

&ldquoPerhaps for things that we took for granted hundreds of years ago as humans, this is not something outside of our grasp just yet. We have this chance here at this national park.&rdquo

Ranger Ben Taylor, Bryce Canyon National Park

However, light pollution even near Bryce Canyon has long been a contested issue with astronomy enthusiasts and local businesses needing to light their parking lots for safety.

While measures have been taken to combat light pollution,

“The enemy of dark skies is basically light pollution, and sometimes coming from a place of ignorance, not appreciating what a rare resource high quality darkness can be,” Poe said.

Lance Syrett, owner of Ruby’s Inn also in Bryce Canyon City, said that on any given night Ruby’s Inn is a “city” of about 4,000 people and manages their light pollution with new light fixtures.

“We don’t do light pollution to be antagonistic,” Syrett said. “We try to be very sensitive to our light, we have a lot of light here that we have to maintain certain safety thresholds … every time we upgrade our lighting we always keep [light pollution] as a consideration.”

Ranger Taylor said light pollution is a tricky issue to balance, but it can be done.

“In some senses it’s like an enemy to natural skies, but it doesn’t have to be. It can be something that’s done productively,” Taylor said.

Visitors at Bryce Canyon National Park this week celebrated the annual Astronomy Festival with lectures, presentations, board displays and stargazing, among other activities. The park earned an official International Dark Sky designation in 2019 but had already been hosting the festival for more than 50 years. (Photo: K. Sophie Will/The Spectrum & Daily News)

Overall, from Taylor to Poe, all astronomy experts say dark skies offer a rare experience for Utahns and should not be taken for granted.

“Perhaps for things that we took for granted hundreds of years ago as humans, this is not something outside of our grasp just yet. We have this chance here at this national park, but if you think about what you can do at home … for making small change, it can really add up,” Taylor said.


Contents

In 1840, François Arago, the director of the Paris Observatory, suggested to Le Verrier that he work on the topic of Mercury's orbit around the Sun. The goal of this study was to construct a model based on Sir Isaac Newton's laws of motion and gravitation. By 1843, Le Verrier published his provisional theory on the subject, which would be tested during a transit of Mercury across the face of the Sun in 1848. Predictions from Le Verrier's theory failed to match the observations. [6]

Despite this, Le Verrier continued his work and, in 1859, published a more thorough study of Mercury's motion. This was based on a series of meridian observations of the planet as well as 14 transits. The rigor of this study meant that any differences from observation would be caused by some unknown factor. Indeed, some discrepancy remained. [6] During Mercury's orbit, its perihelion advances by a small amount, something called perihelion precession. The observed value exceeds the classical mechanics prediction by the small amount of 43 arcseconds per century. [7]

Le Verrier postulated that the excess precession could be explained by the presence of a small planet inside the orbit of Mercury, and he proposed the name "Vulcan" for this object. In Roman mythology, Vulcan is the god of beneficial and hindering fire, [8] including the fire of volcanoes, making it an apt name for a planet so close to the Sun. Today, the International Astronomical Union has reserved the name "Vulcan" for the hypothetical planet, even though it has been ruled out, and also for the vulcanoid population.

Le Verrier's contribution in discovering the planet Neptune in 1846 [9] using the same techniques lent veracity to his claim, and astronomers around the world attempted to find a new planet there, but nothing was ever found.

On 22 December 1859, Le Verrier received a letter from French physician and amateur astronomer Edmond Modeste Lescarbault, who claimed to have seen a transit of the hypothetical planet earlier in the year. Le Verrier took the train to the village of Orgères-en-Beauce, some 70 kilometres (43 mi) southwest of Paris, where Lescarbault had built himself a small observatory. Le Verrier arrived unannounced and proceeded to interrogate the man. [10]

Lescarbault described in detail how, on 26 March 1859, he noticed a small black dot on the face of the Sun, [11] which he was studying with his modest 3.75 inches (95 mm) refractor. Thinking it to be a sunspot, Lescarbault was not at first surprised, but after some time had passed he realized that it was moving. Having observed the transit of Mercury in 1845, he guessed that what he was observing was another transit, but of a previously undiscovered body. He took some hasty measurements of its position and direction of motion, and using an old clock and a pendulum with which he took his patients’ pulses, he estimated the duration of the transit at 1 hour, 17 minutes and 9 seconds. [10]

Le Verrier was satisfied that Lescarbault had seen the transit of a previously unknown planet. On 2 January 1860 he announced the discovery of Vulcan to a meeting of the Académie des Sciences in Paris. Lescarbault, for his part, was awarded the Légion d'honneur and invited to appear before numerous learned societies. [12]

Not everyone accepted the veracity of Lescarbault's "discovery", however. An eminent French astronomer, Emmanuel Liais, who was working for the Brazilian government in Rio de Janeiro in 1859, claimed to have been studying the surface of the Sun with a telescope twice as powerful as Lescarbault's at the very moment that Lescarbault said he observed his mysterious transit. Liais, therefore, was "in a condition to deny, in the most positive manner, the passage of a planet over the sun at the time indicated". [13]

Based on Lescarbault's "transit", Le Verrier computed Vulcan's orbit: it supposedly revolved about the Sun in a nearly circular orbit at a distance of 21 million kilometres (0.14 AU 13,000,000 mi) The period of revolution was 19 days and 17 hours, and the orbit was inclined to the ecliptic by 12 degrees and 10 minutes (an incredible degree of precision). As seen from the Earth, Vulcan's greatest elongation from the Sun was 8 degrees. [10]

Numerous reports—all of them unreliable—began to reach Le Verrier from other amateurs who claimed to have seen unexplained transits. Some of these reports referred to observations made many years earlier, and many could not be properly dated. Nevertheless, Le Verrier continued to tinker with Vulcan's orbital parameters as each new reported sighting reached him. He frequently announced dates of future Vulcan transits, and when these failed to materialize, he tinkered with the parameters some more.

Among the earlier alleged observers of Vulcan:

    reported 'an opaque body traversing the suns disc' on 6 January 1818. [14] , on 26 June 1819, reported seeing "two small spots. on the Sun, round, black and unequal in size" [15] , on 23 October 1822, 24 and 25 July 1823, six times in 1834, on 18 October 1836, 1 November 1836 and on 16 February 1837, also claimed to have seen two spots the larger was 3 arcseconds across, and the smaller 1.25 arcseconds. [15]

Shortly after eight o'clock on the morning of 29 January 1860, F.A.R. Russell and three other people in London saw an alleged transit of an intra-Mercurial planet. [16] An American observer, Richard Covington, many years later claimed to have seen a well-defined black spot progress across the Sun's disk around 1860, when he was stationed in Washington Territory. [17]

No "observations" of Vulcan were made in 1861. Then, on the morning of 20 March 1862, between eight and nine o’clock Greenwich Time, another amateur astronomer, a Mr. Lummis of Manchester, England, saw a transit. His colleague, whom he alerted, also saw the event. [18] Based on these two men's reports, two French astronomers, Benjamin Valz and Rodolphe Radau, independently calculated the object's supposed orbital period, with Valz deriving a figure of 17 days and 13 hours and Radau a figure of 19 days and 22 hours. [19]

On 8 May 1865 another French astronomer, Aristide Coumbary, observed an unexpected transit from Istanbul, Turkey. [20]

Between 1866 and 1878 no reliable observations of the hypothetical planet were made. Then, during the total solar eclipse of July 29, 1878, two experienced astronomers, Professor James Craig Watson, the director of the Ann Arbor Observatory in Michigan, and Lewis Swift, an amateur from Rochester, New York, both claimed to have seen a Vulcan-type planet close to the Sun. Watson, observing from Separation, Wyoming, placed the planet about 2.5 degrees southwest of the Sun and estimated its magnitude at 4.5. Swift, who was observing the eclipse from a location near Denver, Colorado, saw what he took to be an intra-mercurial planet about 3 degrees southwest of the Sun. He estimated its brightness to be the same as that of Theta Cancri, a fifth-magnitude star which was also visible during totality, about six or seven minutes from the "planet". Theta Cancri and the planet were very nearly in line with the centre of the Sun.

Watson and Swift had reputations as excellent observers. Watson had already discovered more than twenty asteroids, while Swift had several comets named after him. Both described the colour of their hypothetical intra-mercurial planet as "red". Watson reported that it had a definite disk—unlike stars, which appear in telescopes as mere points of light—and that its phase indicated that it was approaching superior conjunction. [ citation needed ]

Both Watson and Swift had actually observed two objects they believed were not known stars, but after Swift corrected an error in his coordinates, none of the coordinates matched each other, nor known stars. The idea that four objects were observed during the eclipse generated controversy in scientific journals, and mockery from Watson's rival, C. H. F. Peters. Peters noted that the margin of error in the pencil and cardboard recording device Watson had used was large enough to plausibly include a bright known star. A skeptic of the Vulcan theory, Peters dismissed all the observations as mistaking known stars as planets. [21] : 215–217

Astronomers continued searching for Vulcan during total solar eclipses in 1883, 1887, 1889, 1900, 1901, 1905, and 1908. [21] : 219

Outside of eclipses, many false alarms were triggered by round sunspots that closely resembled planets in transit. [ citation needed ]

In 1915 Einstein's theory of relativity, an approach to understanding gravity entirely different from classical mechanics, solved the problem. [3] His equations predicted exactly the observed amount of advance of Mercury's perihelion without any recourse to the existence of a hypothetical Vulcan. The new theory modified the predicted orbits of all planets, but the magnitude of the differences from Newtonian theory diminishes rapidly as one gets farther from the Sun. Also, Mercury's fairly eccentric orbit makes it much easier to detect the perihelion shift than is the case for the nearly circular orbits of Venus and Earth.

Einstein's theory was empirically verified during the solar eclipse of May 29, 1919 by measuring the bending of sunlight. Astronomers generally quickly accepted that a large planet inside the orbit of Mercury could not exist, given the corrected equation of gravity. [21] : 220

Observing a planet inside the orbit of Mercury is difficult, since the telescope must be pointed very close to the Sun, where the sky is only dark during a solar eclipse. Also, an error in pointing the telescope can result in damage for the optics, and injury to the observer if viewing directly. The huge amount of light present even quite far away from the Sun can produce false reflections inside the optics, thus fooling the observer into seeing things that do not exist.

The best observational strategy might be to monitor the Sun's disk for possible transits, but transits would only be seen from Earth provided the object orbits close enough to the ecliptic plane. A small, dark spot might be seen to move across the Sun's disk, as happens with transits of Mercury and Venus.

In 1915, when Einstein successfully explained the apparent anomaly in Mercury's orbit, most astronomers abandoned the search for Vulcan. A few, however, remained convinced that not all the alleged observations of Vulcan were unfounded. Among these was Henry C Courten, of Dowling College, New York. Studying photographic plates of the 1970 eclipse of the Sun, he and his associates detected several objects which appeared to be in orbits close to the Sun. [22] Even accounting for artifacts, Courten felt that at least seven of the objects were real.

Courten believed that an intra-Mercurial planetoid between 130 and 180 kilometres (80 and 110 mi) in diameter was orbiting the Sun at a distance of about 0.1 AU (15,000,000 km 9,300,000 mi). Other images on his eclipse plates led him to postulate the existence of an asteroid belt between Mercury and the Sun.

None of these claims has ever been substantiated after more than forty years of observation. It has been surmised that some of these objects—and other alleged intra-Mercurial objects—may exist, being nothing more than previously unknown comets or small asteroids. No vulcanoid asteroids have been found, and searches have ruled out any such asteroids larger than about 6 km (3.7 mi). [4] Neither SOHO nor STEREO has detected a planet inside the orbit of Mercury. [4] [23]


Researchers Have Identified 100 Mysteriously Disappeared Stars in The Night Sky

Across the Milky Way there are vacant spaces where a star once brightly shone. Some left clues in a dramatic death, or faded into retirement. Others simply moved into a new neighbourhood.

Not all vacancies have such convenient explanations, though. Some were there one moment and gone the next, inviting speculation over rare types of star death, extreme astrophysics, and, of course… advanced alien technology.

By comparing star catalogues dating back to the 1950s with more recent datasets, researchers with the Vanishing & Appearing Sources during a Century of Observations project have identified around 100 bright dots that seem to have vanished without a trace.

The search is an ongoing one for lead researcher Beatriz Villarroel and her colleagues, one that started several years ago as part of a hunt for potential signs of alien intelligence.

"Finding an actually vanishing star – or a star that appears out of nowhere! – would be a precious discovery and certainly would include new astrophysics beyond the one we know of today," says Villarroel, a theoretical physicist from Stockholm University.

In an earlier study Villarroel and her team compared the positions of some 10 million objects recorded in the US Naval Observatory Catalogue (USNO) with their counterparts in the Sloan Digital Sky Survey (SDSS).

They were left with about 290,000 missing objects, most of which could easily be accounted for on closer inspection. Eventually they found a single star that genuinely seemed to have disappeared, and even that discovery came with lingering doubts.

It was an intriguing find, but hardly constituted compelling evidence of new kinds of astrophysics.

In this latest study they compared 600 million objects in the USNO catalogue with a collection put together by the University of Hawaii's Pan-STARR system.

The naval catalogue spans around 50 years of sky surveys, capturing details of the entire sky in five colours down to a visual magnitude of about 21. The cosmic objects in the Pan-STARR data release include slightly dimmer objects, down to a magnitude of roughly 23 as compared to the SDSS's 22.

Having more stars to compare means potentially more 'missing' stars, while capturing objects of a lower magnitude means making extra sure there's nothing sitting in the star's place.

The comparison revealed 151,193 candidates for missing stars. This number was whittled down to 23,667 possibilities by widening the search field, cutting away stars that seemed to have moved farther than expected.

That short list was visually inspected, excluding around 18,000 images that were messed up by flaws or artefacts. Lastly, the team removed images where the missing star was towards the edge of the field, just to reduce risk of any false positives.

One final sweep using yet another method for comparisons removed other possible flaws in data collection, or unclear results. That left 100 dark shadows where a star once shone.

When a star dies, it usually goes out with a bright shout as a super nova, or quietly fades into a softly glowing ember like a white dwarf. They don't tend to just stop shining.

There could be some clues in the fact that the pool of candidates were in general a little redder in colour than the typical USNO catalogue object, and were generally faster moving. Working it out will take further research.

"We are very excited about following up on the 100 red transients we have found," says Villarroel.

There are plenty of explanations that need exploring before we can be confident this represents anything exotic, something the team hopes to accomplish with citizen science projects.

One possibility is that the object occasionally flares enough to be seen before dimming again a few magnitudes. Another explanation – although very unlikely – is they're all just scratches after all, and never existed to begin with. It could also be a dull star we assumed was farther away and has just moved too far to be noticed.

A more exciting thought is that a few might be super-rare failed supernovas, forming black holes without the fireworks display. As cool as that would be, it's a stretch to think this would explain all of the observations.

If the disappeared stars turn out to be none of these things, we may need to entertain new physics.

"We believe that they are natural, if somewhat extreme, astrophysical sources," says Martin López Corredoira from the Instituto de Astrofísica de Canarias in the Canary Islands.

There is that other explanation. The one we'd all like to be true, but can't take seriously until we have a lot more evidence: Aliens could be covering these stars up to absorb their light, converting it into useful energy before shedding it as low grade radiation. Or the initial flares might be short lived, intense signals from alien technology.

In moments like this, we can all let our imaginations run a little wild, even if the researchers are hesitant.

"But we are clear that none of these events have shown any direct signs of being ETI [extra terrestrial intelligence]," says Corredoira.


Vulcanoid asteroid

Vulcanoids are hypothetical group of asteroids that may orbit in a dynamically stable zone between 0.08 and 0.21 astronomical units from the Sun, well within the orbit of Mercury. They take their name from the hypothetical planet Vulcan, which nineteenth-century astronomers fruitlessly searched for to explain the excess precession of Mercury's perihelion. Virtually all the anomaly in Mercury's orbit later turned out to be an effect explained by general relativity, removing the need to postulate the existence of Vulcan.

The hypothesis that there could be such a population of asteroids was put forward by Charles Dillon Perrine, one of the most active observational astronomers of that time. But despite more than a century of searching since the 1901 eclipse, no Vulcanoids have ever been found, despite ground-based searches and more recent searches by NASA using high-altitude F-18 aircraft and Black Brant suborbital rockets. Such searches are extremely difficult due to the glare of the Sun. Additionally, the space-based Solar and Heliospheric Observatory (SOHO) would have been able to see any bright objects near the Sun (for example, it has seen hundreds of small comets). If Vulcanoids exist, for the expected albedo they cannot be more than 60 km in diameter, since previous searches would have found anything larger. Vulcanoid asteroids, if they exist, would be a special subclass of Apohele asteroids.

Nevertheless, it is thought Vulcanoids could exist because the region of space being searched is gravitationally stable. Also, the heavily cratered surface of Mercury means a population of Vulcanoids probably existed in the very early days of the solar system. Over long timescales, the orbits of Vulcanoids are not completely stable, due to the Yarkovsky effect. The dynamical lifetime of a Vulcanoid is measured in tens of millions of years, and according to David Vokrouhlicky, Paolo Farinella and William F. Bottke, Jr. the vulcanoid population would have been depleted within a billion years of the formation of Mercury. According to their 2000 paper, there should be no original Vulcanoids left, having either impacted Mercury or been drawn into the Sun. They also argue that the current data on bombardment indicates that Mercury, to the extent it is mapped, does not show a signature pattern of cratering which would indicate that Vulcanoids ever existed. However, they speculate that a small population could exist within available measurements, though better data of the Mercurian surface would be required to establish this.

Future searches for Vulcanoids will likely use small space-based telescopes, which can see very close to the Sun. SOHO is not the best instrument for the task, but suitable spacecraft have been proposed to look for near-Earth objects. Indirect evidence for Vulcanoids may come from the MESSENGER probe, which is scheduled to fly by Mercury three times and then insert into a planetary orbit.

The entire inner solar system is not well explored, with only one probe having visited Mercury: Mariner 10, which managed to photograph 45% of the planet in a series of fly-bys in 1973 and 1974.


Discover Interview: Planetary Scientist Alan Stern

This summer, construction will begin on a probe to Pluto and the Kuiper belt. Planetary scientist Alan Stern, director of the Southwest Research Institute in Boulder , Colorado , is the principal investigator for the mission. He is also a licensed commercial pilot and was once a finalist for the position of space shuttle mission specialist. Stern has made a career of investigating the solar system’s frontiers, from a mysterious band of asteroids that may be orbiting the sun inside Mercury to the vast Oort cloud far beyond the known planets, the source of all comets.

Did you ever think that a mission to Pluto wouldn’t happen?

I had a lot of doubts through the 1990s, during Dan Golden’s NASA administration, because NASA repeatedly cancel l ed missions to Pluto, despite the fact that the scientific community kept saying it was top priority, crucial to getting an understanding of our solar system. Now I am fairly convinced that it will happen.

S: Of course it is a planet. The generally accepted definition of a planet is very simple: It is a body that orbits its star, and it has to be large enough to become round under self-gravity but not so large that hydrogen fusion takes place in its center. If the object is too large and fusion takes place, we call it a star. And if it’s too small and its own gravity wouldn’t make it round, we call it a rock. Pluto is about 10 times the size of the smallest object in space that would become round due to gravity, so it easily qualifies.

S: In part, we should go because exploration is part of what makes us human. Beyond that, we should go because it turns out that Pluto is at the nexus of four key scientific themes that will lead us to a better understanding of our solar system. One theme is that Pluto was the first to be discovered of an enormous collection of trans-Neptunian objects called the Kuiper belt. These bodies are part of a previously unknown portion of the solar system—what I like to call the third zone of the solar system. This third zone was on its way to growing a very large planet, but something—we don’t know what—stopped the process. Instead we have a collection of miniature planets. That means that in this zone we can find planetary embryos that were frozen in time during their gestation. That gives us a window into the past. That’s the second theme.

The third theme is that Pluto and its moon, Charon, which is half Pluto’s size, constitute a binary planet. We think binary planets are common in the galaxy, just as we know that binary stars are common in the galaxy, and we have even begun to find binary asteroids. The New Horizons Pluto mission will be the first mission to a binary object and will help us understand everything from the origin of Earth’s moon to the physics of mass transfer between binary stars.

Finally, Pluto has a knock-your-socks-off atmosphere that’s escaping rapidly like a comet’s, but on a planetary scale. As a result, the planet has shrunk in size over billions of years because of the same processes that shaped the early evolution of Earth’s atmosphere and very likely that of both Mars and Venus. We have never been to a planet where this kind of rapid escape is taking place. By going to Pluto we have a chance to anchor, with real data, models of the early evolution of Earth’s atmosphere.

What would people see if they went to Pluto and stood on the surface?

S: The surface is bright and covered in a fresh, pinkish snow. People commonly think that it would be dark on Pluto because it is so far from the sun, but it is actually about as bright as dusk here on Earth, with enough light for you to very easily read a book and see what’s going on around you. On the Charon side of Pluto, you’d see a big old moon up in the sky, appearing 10 times as wide as Earth’s moon and twice as bright. You might see mountains on Pluto. You’d certainly see craters. There may be volcanoes and geysers. You would from time to time see atmospheric phenomena such as fog, clouds, or hazes. If you were there long enough, you would see it snow.

What is the third zone of the solar system like?

S: The Kuiper belt region, which I call the third zone because it lies beyond the rocky terrestrial planets and beyond the giant planets, is a bizarre frontier. It is dotted by more than 100,000 miniature frozen worlds. Based on data already in hand, we suspect that most are made of rock and ice with a liberal dash of organic molecules. It appears that thousands of these bodies have moons. Some may even occasionally grow atmospheres. And the latest news is that the king of the Kuiper belt, the king of the third zone, Pluto, may even sport an ocean under its icy crust!

How much is out there at the edge of our solar system that we have not yet discovered?

S: The short answer is—a lot. The Kuiper belt is probably littered with hundreds, if not thousands, of ice-dwarf planets like Pluto. NASA has explored all four terrestrial planets and all four giant planets. But the number of bodies we’d classify as planets in the solar system is probably closer to 9,000 than it is to nine, and we haven’t been to the most populous class of bodies at all—the ice-dwarf planets of the Kuiper belt. Even farther out, beyond the Kuiper belt, lies the Oort cloud, 1,000 times farther away. The Oort cloud consists of objects ejected from the region surrounding the giant planets during and after their formation. In the Oort cloud there may be large planets that were ejected from the solar system in the early days when Jupiter, Saturn, Uranus, and Neptune were muscling out their rivals.

Could there be objects as big as Jupiter or Saturn in the region beyond Pluto?

S: Not objects the size of Jupiter or Saturn because Jupiter and the other giant planets couldn’t have ejected objects that large, but there certainly could be a handful of Earth- and Mars-size objects. There could be hundreds of things the size of Pluto in the Oort cloud, and a number of objects the size of

You have to look! Actually, anything in the Oort cloud is too faint to see with the technology we have today. For example, NASA’s Spitzer Space Telescope, which launched in August

, can see an object the size of Pluto located a few hundred astronomical units away [

one astronomical unit is 96 million miles—the distance from

, and Spitzer can detect a planet the size of Earth out to about 1,000 astronomical units. However, the Oort cloud is between 10,000 and 100,000 astronomical units away. So an Oort cloud survey will have to be the project of a future generation.

Can studying Pluto and these other objects tell us anything about Earth’s formation and its history?

S: Yes, it can. The standard model for the formation of the Earth-moon system is that a huge, Mars-size object hit Earth and spun off material that coalesced in orbit to become the moon. The Pluto-Charon system is the only other place in our solar system where we believe this happened on a planetary scale. By going to a system like Pluto-Charon, we’ll better understand how the Earth-moon system formed.

After Pluto, where else in the solar system would you like to explore?

S: I would like to see a robotic return mission to Uranus and Neptune. I’d like to see further robotic exploration of the Kuiper belt, and I’d like particularly to see humans go back to the moon for a serious exploration and then on to asteroids and Mars.

S: The vulcanoids are a putative population of asteroids that may circle the sun inside the orbit of Mercury, like a little Kuiper belt, if you will, on the inside of the solar system. Instead of being icy, however, they are expected to be rocky because it is so hot. Although no object on such an orbit has been detected just yet, there is good reason to expect that they might exist. For example, the surface of Mercury is severely battered, and many of the projectiles that hit it may have been vulcanoids. The question is whether there are any left or whether they’re all gone. We really don’t know because it’s a very, very difficult observational problem to detect these bodies, even with modern technology. The easiest way to look is from space, but that’s very expensive. Doing it from the ground is extremely hard because one has to look for faint points of light against the twilight sky. Our group has taken a middle-ground approach by using high-altitude aircraft that can fly up into the high upper stratosphere where the sky is much darker, making the vulcanoids easier to detect. We haven’t finished our search yet, so I can’t yet tell you if there are vulcanoids. Stay tuned!

You’ve done these vulcanoid surveys and studies of other asteroids, meteors, and comets from the backseat of a high-performance aircraft, like a WB-57 or a F/A-18 Hornet fighter jet. Is there really a scientific benefit to working out of an F-18, or is it just a lot of fun?

S: It’s both. I have to say that the grants that paid for the studies came through peer-review panels that throw out five of every six proposals. If this was purely so that I could have a good time in the backseat of a fighter, it wouldn’t survive for 10 minutes in a peer-review panel.

My colleague Daniel Durda and I discovered a way to do certain kinds of astronomy from a jet that you just cannot do from the ground. You can do these studies from space, but this is 1,000 times cheaper, and 10 times cheaper than using a big aircraft like those NASA typically has flown around. And for the particular niche we are exploring, the jets we use do the trick.

As a pilot, do you ever get the itch to take the controls?

S: Every flight. Sometimes we even get to. But the mission isn’t to let the astronomer fly it’s to accomplish specific observing goals with the gear we bring along.

Why do you focus on the solar system’s small, low-profile bodies? Why not big-ticket items like Mars?

S: The smaller objects are big-ticket items! Understanding the architecture of our solar system is a pretty big-ticket item. Discovering whether or not there is an asteroid belt interior to Mercury’s orbit, finding out whether or not the comets were crucial to the formation to life on Earth, doing the first mission to the last planet, Pluto—I consider these all big-ticket items. Just because Pluto or comets aren’t as big as Jupiter doesn’t mean they are not scientifically important—indeed, just the reverse is often true. Sometimes great things come in small packages.

But, honestly, the public just isn’t that interested in comets or the Kuiper belt. Most people have never heard of vulcanoids.

S: I think you’re right about the vulcanoids, but there are a lot of things people have never heard of that eventually come to be very important. Six hundred years ago, most people never heard of North America. Being a researcher doesn’t mean that you follow what is publicly appealing, because public interest generally lags scientific understanding. It’s our responsibility as research explorers to find out the lay of the land, not to follow a popularity contest about where our research should go.

What’s the most important thing about astronomy that everyone should know but don’t?

S: I’d say how ancient virtually everything is in space. Almost all of the galaxies, the stars, the planets, are billions of years old—a million times older than the Parthenon, and tens of millions of times older than the oldest human being who has ever lived. To me, that really puts a lot of things that happen in day-to-day life, or the news, in perspective. No matter how old you are, it makes you feel young. And—perhaps this is the best part—it makes you realize how audacious we are as a species that was “born yesterday” to think we can understand the universe!

What are we learning about comets?

S: Comets are very important in terms of the hazard they pose to Earth’s ecosystems over geological time, and they’re the best samples we have of the primordial material that formed the solar system. We know that comets bombarded Earth after its formation, and they brought a lot of water and more complex stuff to the young planet. Although I personally discount it, it is entirely possible that comets actually brought life to Earth—microspores or something from other systems where life had evolved. We won’t know until we bring back samples.

Many researchers who work on unmanned space projects take issue with all the money that goes into manned missions. You’ve worked both sides of the street. What’s your take?

S: NASA’s human exploration program did historic, even epic, things in the 1960s and early 1970s, but it has been on a leash ever since. We have the capability to do so much more, to do real geological field exploration of the moon and the asteroids and field expeditions to Mars. Instead, for the past three decades we’ve been relegated to nothing more than trips to low Earth orbit in space shuttles and a space station going around in circles growing plants and taking pictures of the weather. I hope that will change soon.

S: The political will hasn’t been there, and it’s so unfortunate. I think human beings are truly explorers at heart. The planets are the obvious next frontiers for human exploration. There’s no reason that we shouldn’t have a significant number of people living and working on the moon, doing geological studies of asteroids and pioneering the path to Mars. The technology is well in hand.

You’re not concerned about the dangers?

S: Of course I am, but danger is an integral part of true exploration. If you’ve ever been around aerospace vehicles, you know that a human being can get hurt in those big machines. Explorers 500 years ago faced a similar question: Is it too risky to sail to some unknown land in a rickety boat at the mercy of the wind? But look at what those daring explorations brought us in terms of the changes to the world. To be a great nation in the 21st century, the United States needs to explore the space frontier. If we choose this course, the road will be long and hard—and yes, dangerous. But so were the frontiers that this great nation took as previous challenges during the 18th, 19th, and 20th centuries. We should make a lasting commitment to the exploration of the moon and planets by both brave humans and sophisticated robots. We should inspire the world, and we should make history again. It’s something America does extremely well.

If you could go anywhere in the solar system for one week, where would you go?

S: I’d like to spend a week exploring Neptune’s giant moon, Triton. The Neptunian system is a scientist’s playground. Triton seems to be geologically active like there’s no tomorrow, even though it’s only 40 degrees above absolute zero there. To conduct a field operation on Triton would be beyond my wildest imagination.