Gaia mapping the stars of the Milky Way. Credit: ESA/ATG medialab; background: ESO/S. Brunier
In 2013, the European Space Agency (ESA) deployed the Gaia mission, a space observatory designed to measure the positions of movements of celestial bodies. For the past four years, Gaia has been studying distant stars, planets, comets, asteroids, quasars and other astronomical objects, and the data it has acquired will be used to construct the largest and most precise 3D space catalog ever made, totaling 1 billion objects.
Using data provided by Gaia, a team of international scientists conducted a study of the recently-discovered star cluster known as Gaia 1. Located about 15,000 light years from Earth and measuring some 29 light years in radius, much about this cluster has remained unknown. As such, this study helped place constraints on a number of mysteries of this star cluster, which include its age, metallicity and origin.
For the sake of their study, which recently appeared in the journal Astronomy and Astrophysics under the title “Detailed Chemical Abundance Analysis of the Thick Disk Star Cluster Gaia 1“, the team conducted a detailed chemical abundance study of Gaia 1 to determine its unknown parameters. From this, accurate estimates on its age and composition are likely to now be possible.
Sky map based on the first release of Gaia data (DR1). Credit: ESA/Gaia/DPAC/A. Moitinho & M. Barros, CENTRA – University of Lisbon.
This combined photometry also indicated that the cluster had a radius of about 29 light years and contained as much as 20,000 Solar Masses. However, further studies found that the cluster was actually far more metal-rich than previously thought. This indicated that Gaia 1 was likely to be significantly younger, with estimates now claiming that it was at least 3 billion years old.
In addition, these subsequent studies also raised the possibility that the cluster was extra-galactic in origin, based on the fact that it orbits about 5,500 light years (~1.7 kpc) above the Milky Way’s disk. To remedy this, the team – led by Andreas Koch of the University of Lancaster and the Center for Astronomy Heidelberg – used Gaia data in order to conduct a detailed study of just how metal-rich the cluster was to get a better idea of its age.
As they stated in their study: “[T]his work focuses on a detailed chemical abundance analysis of four red giant members of Gaia 1, based on high-resolution spectroscopy, which we complement by an investigation of the orbital properties of this transition object.” This consisted of measuring the abundances of 14 elements within these red giant stars, which were selected from the 2MASS survey.
What they determined was that the Gaia 1 was more metal poor than previously expected, which indicated that it is older than the revised age estimates indicated – between 3 billion and 5.3 billion years old. In addition, they also measured the proper motions and orbits of the four target stars, using data obtained from the fifth U.S. Naval Observatory CCD Astrograph Catalog (UCAC5).
This information revealed that in the course of their orbits, the four target stars would reach a maximum distance of 3,262 light years (1.0 kpc) above the galactic disk, which was an indication that they were not extra-galactic in origin. Last, but not least, they indicated that Gaia 1’s structure does not truly conform to that of a globular cluster, as it was originally designated. As they conclude in their study:
“This confirms that Gaia 1 is rather a massive and luminous open cluster than a low-mass globular cluster. Finally, orbital computations of the target stars bolster our chemical findings of Gaia 1’s present-day membership with the thick disk, even though it remains unclear, which mechanisms put it in that place.”
While this study has helped place constraints on one of a newly-discovered Gaia object, the team acknowledges that there is still much to be discovered about this star cluster. They also acknowledge that there is a margin of error when it comes to their study, and that further research is needed before Gaia 1 can be properly classified.
The band of light (the Milky Way) that is visible in the night sky, showing the stellar disk of our galaxy. Credit: Bob King
“However, the hint of a metallicity spread between different studies in the literature may point towards a more complex origin that could involve a once more massive progenitor,” they state. “Thus the question as to its exact formation and origin remains unclear and needs to await more data such as the precise and accurate parallaxes that Gaia can offer.”
This newly-discovered cluster, and all attempts to better understand it, are merely the tip of the iceberg when it comes to what the Gaia mission has revealed so far. The second official release of Gaia data – aka. Gaia DR2 – is scheduled to take place in April of 2018. This will be followed by a third release in 2020 and, barring any mission extensions, a fourth and final release in 2022.
Hubble image of the Ring Nebula (aka. Messier 57). Credit: NASA/ESA/ Hubble Heritage (STScI/AURA) – ESA /Hubble Collaboration
Welcome back to Messier Monday! We continue our tribute to our dear friend, Tammy Plotner, by looking at the the Big Ring itself, the planetary nebula known as Messier 57. Enjoy!
In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list – known as the Messier Catalog – would go on to serve a more important function.
One of these objects is known as Messier 57, a planetary nebula that is also known as the Ring Nebula. This object is located about 2,300 light years from Earth in the direction of the Lyra constellation. Because of its proximity to Vega, the brightest star in Lyra and one of the stars that form the Summer Triangle, the nebula is relatively easy to find using binoculars or a small telescope.
What You Are Looking At:
Here you see the remainders of a sun-like star… At one time in its life, it may have had twice the mass of Sol, but now all that’s left is a white dwarf that burns over 100,000 degrees kelvin. Surrounding it is an envelope about 2 to 3 light years in size of what once was its outer layers – blown away in a cylindrical shape some 6000 to 8000 years ago. Like looking down the barrel of a smoking gun, we’re looking back in time at the end of a Mira-like star’s evolutionary phase.
It’s called a planetary nebula, because once upon a time before telescopes could resolve them, they appeared almost planet-like. But, as for M57, the central star itself is no larger than a terrestrial planet! The tiny white dwarf star, although it could be as much as 2300 light years away, has an intrinsic brightness of about 50 to 100 times that of our Sun.
One of the most beautiful features of M57 is the structure in the ring itself, sometimes called braiding – but scientifically known as “knots” in the gaseous structure. As C.R. O’Dell (et al) indicated in their 2003 study:
“We have studied the closest bright planetary nebulae with the Hubble Space Telescope’s WFPC2 in order to characterize the dense knots already known to exist in NGC 7293. We find knots in all of the objects, arguing that knots are common, simply not always observed because of distance. The knots appear to form early in the life cycle of the nebula, probably being formed by an instability mechanism operating at the nebula’s ionization front. As the front passes through the knots they are exposed to the photoionizing radiation field of the central star, causing them to be modified in their appearance. This would then explain as evolution the difference of appearance like the lacy filaments seen only in extinction in IC 4406 on the one extreme and the highly symmetric “cometary” knots seen in NGC 7293. The intermediate form knots seen in NGC 2392, NGC 6720, and NGC 6853 would then represent intermediate phases of this evolution.”
However, examining things like planetaries nebulae in different wavelengths of light can tell us so much more about them. Behold the beauty when see through the Spitzer Space Telescope! As M.M. Roth explained in a 2007 study:
“Emission nebulae like H II regions, Planetary Nebulae, Novae, Herbig Haro objects etc. are found as extended objects in the Milky Way, but also as point sources in other galaxies, where they are sometimes observable out to very large distances due to the high contrast provided by some prominent emission lines. It is shown how 3D spectroscopy can be used as a powerful tool for observations of both large resolved emission nebulae and distant extragalactic objects, with special emphasis on faint detection limits.”
History of Observation:
This deep space object was first discovered in early January 1779 by Antoine Darquier who wrote in his notes:
“This nebula, to my knowledge, has not yet been noticed by any astronomer. One can only see it with a very good telescope, it is not resembling any of those [nebula] already known; it has the apparent dimension of Jupiter, is perfectly round and sharply limited; its dull glow resembles the dark part of the Moon before the first and after the last quarter. Meanwhile, the center appears a bit less pale than the remaining part of its surface.”
Although Darquier did not post a date, it is believed his observation preceded Messier’s independent recovery made on January 31, 1779 when he states that Darquier picked it up before him:
“A cluster of light between Gamma and Beta Lyrae, discovered when looking for the Comet of 1779, which has passed it very close: it seems that this patch of light, which is round, must be composed of very small stars: with the best telescopes it is impossible to distinguish them; there stays only a suspicion that they are there. M. Messier reported this patch of light on the Chart of the Comet of 1779. M. Darquier, at Toulouse, discovered it when observing the same comet, and he reports: ‘Nebula between gamma and beta Lyrae; it is very dull, but perfectly outlined; it is as large as Jupiter and resembles a planet which is fading’.”
A few years later, Sir William Herschel would also observe Messier Object 57 with his superior telescope and in his private notes he writes:
“Among the curiosities of the heavens should be placed a nebula, that has a regular, concentric, dark spot in the middle, and is probably a Ring of stars. It is of an oval shape, the shorter axis being to the longer as about 83 to 100; so that, if the stars form a circle, its inclination to a line drawn from the sun to the center of this nebula must be about 56 degrees. The light is of the resolvable kind [i.e., mottled], and in the northern side three very faint stars may be seen, as also one or two in the southern part. The vertices of the longer axis seem less bright and not so well defined as the rest. There are several small stars very bear, but none seems to belong to it.”
Admiral Smyth would go on in later years to add his own detailed observations to history’s records:
“This annular nebula, between Beta and Gamma on the cross-piece of the Lyre, forms the apex of a triangle which it makes with two stars of the 9th magnitude; and its form is that of an elliptic ring, the major axis of which trends sp to nf [SW to NE]. This wonderful object seems to have been noted by Darquier, in 1779; but neither he nor his contemporaries, Messier and Méchain, discerned its real form, seeing in this aureola of glory only “a mass of light in the form of a planetary disc, very dingy in colour.”
“Sir W. Herschel called it a perforated resolvable nebula, and justly ranked it among the curiosities of the heavens. He considered the vertices of the longer axis less bright and not so well defined as the rest; and he afterwards added: ‘By the observations of the 20-feet telescope, the profundity of the stars, of which it probably consists, must be of a higher than the 900th order, perhaps 950.'”
“This is a vast view of the ample and inconceivable dimensions of the spaces of the Universe; and if the oft-cited cannon-ball, flying with the uniform velocity of 500 miles an hour, would require millions of years to reach Sirius, what an incomprehensible time it would require to pass so overwhelming an interval as 950 times the distance! And yet, could we arrive there, by all analogy, no boundary would meet the eye, but thousands and ten thousands of other remote and crowded systems would still bewilder the imagination.
“In my refractor this nebula has a most singular appearance, the central vacuity being black, so as to countenance the trite remark of its having a hole through it. Under favourable circumstances, when the instrument obeys the smooth motion of the equatorial clock, it offers the curious phenomenon of a solid ring of light in the profundity of space. The annexed sketch affords a notion of it. Sir John Herschel, however, with the superior light of his instrument, found that the interior is far from absolutely dark. “It is filled,’ he says, ‘with a feeble but very evident nebulous light, which I do not remember to have been noticed by former observers.'”
Since Sir John’s observation, the powerful telescope of Lord Rosse has been directed to this subject, and under powers 600, 800, and 1000, it displayed very evident symptoms of resolvability at its minor axis. The fainter nebulous matter which fills it, was found to be irregularly distributed, having several stripes or wisps in it, and the regularity of the outline was broken by appendages branching into space, of which prolongations the brightest was in the direction of the major axis.
Locating Messier 57:
M57 is a breeze to locate because it is positioned between Beta and Gamma Lyrae (the westernmost pair of the lyre’s stars), at about one-third the distance from Beta to Gamma. While it is easily seen in binoculars, it is a little difficult to identify because of its small size, so binoculars must be very steady to distinguish it from the surrounding star field.
In even a small telescope at minimum power, you’ll quickly notice a very small, but perfect ring structure which takes very well to magnification. Despite low visual brightness, M57 actually takes well to urban lighting conditions and can even be spied during fairly well moonlit nights. Larger aperture telescopes will easily see braiding in the nebula structure and often glimpse the central star. May you also see the many faces of the “Ring”!
The location of Messier 57 in the Lyra Constellation. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
And here are the quick facts on Messier 57 to help you get started:
Object Name: Messier 57 Alternative Designations: M57, NGC 6720, the “Ring Nebula” Object Type: Planetary Nebula Constellation: Lyra Right Ascension: 18 : 53.6 (h:m) Declination: +33 : 02 (deg:m) Distance: 2.3 (kly) Visual Brightness: 8.8 (mag) Apparent Dimension: 1.4×1.0 (arc min)
Artist’s impression shows the binary asteroid 288P, located in the Main Asteroid Belt between the planets Mars and Jupiter. Credit: ESA/Hubble, L. Calçada.
In 1990, the NASA/ESA Hubble Space Telescope was deployed into Low Earth Orbit (LEO). As one of NASA’s Great Observatories – along with the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope – this instrument remains one of NASA’s larger and more versatile missions. Even after twenty-seven years of service, Hubble continues to make intriguing discoveries, both within our Solar System and beyond.
The latest discovery was made by a team of international astronomers led by the Max Planck Institute for Solar System Research. Using Hubble, they spotted a unique object in the Main Asteroid Belt – a binary asteroid known as 288P – which also behaves like a comet. According to the team’s study, this binary asteroid experiences sublimation as it nears the Sun, which causes comet-like tails to form.
Using the Hubble telescope, the team first observed 288P in September 2016, when it was making its closest approach to Earth. The images they took revealed that this object was not a single asteroid, but two asteroids of similar size and mass that orbit each other at a distance of about 100 km. Beyond that, the team also noted some ongoing activity in the binary system that was unexpected.
As Jessica Agarwal explained in a Hubble press statement, this makes 288P the first known binary asteroid that is also classified as a main-belt comet. “We detected strong indications of the sublimation of water ice due to the increased solar heating – similar to how the tail of a comet is created,” she said. In addition to being a pleasant surprise, these findings are also highly significant when it comes to the study of the Solar System.
Since only a few objects of this type are known, 288P is an extremely important target for future asteroid studies. The various features of 288P also make it unique among the few known wide asteroid binaries in the Solar System. Basically, other binary asteroids that have been observed orbited closer together, were different in size and mass, had less eccentric orbits, and did not form comet-like tails.
The observed activity of 288P also revealed a great deal about the binary asteroids past. From their observations, the team concluded that 288P has existed as a binary system for the past 5000 years and must have accumulated ice since the earliest periods of the Solar System. As Agarwal explained:
“Surface ice cannot survive in the asteroid belt for the age of the Solar System but can be protected for billions of years by a refractory dust mantle, only a few meters thick… The most probable formation scenario of 288P is a breakup due to fast rotation. After that, the two fragments may have been moved further apart by sublimation torques.”
Image depicting the two areas where most of the asteroids in the Solar System are found: the Main Asteroid Belt and the Trojans. Credit: ESA/Hubble, M. Kornmesser
Naturally, there are many unresolved questions about 288P, most of which stem from its unique behavior. Given that it is so different from other binary asteroids, scientists are forced to wonder if it merely coincidental that it presents such unique properties. And given that it was found largely by chance, it is unlikely that any other binaries that have similar properties will be found anytime soon.
“We need more theoretical and observational work, as well as more objects similar to 288P, to find an answer to this question,” said Agarwal. In the meantime, this unique binary asteroid is sure to provide astronomers with many interesting opportunities to study the origin and evolution of asteroids orbiting between Mars and Jupiter.
In particular, the study of those asteroids that show comet-like activity (aka. main-belt comets) is crucial to our understanding of how the Solar System formed and evolved. According to contrasting theories of its formation, the Asteroid Belt is either populated by planetesimals that failed to become a planet, or began empty and gradually filled with planetesimals over time.
In either case, studying its current population can tell us much about how the planets formed billions of years ago, and how water was distributed throughout the Solar System afterwards. This, in turn, is crucial to determining how and where life began to emerge on Earth, and perhaps elsewhere!
Be sure to check out this animation of the 288P binary asteroid too, courtesy of the ESA and Hubble:
An artist's impression of the cosmic web, the filamentary structure that fills the entire Universe. Credit: M. Weiss/CfA
When astronomers first noted the detection of a Fast Radio Burst (FRB) in 2007 (aka. the Lorimer Burst), they were both astounded and intrigued. This high-energy burst of radio pulses, which lasted only a few milliseconds, appeared to be coming from outside of our galaxy. Since that time, astronomers have found evidence of many FRBs in previously-recorded data, and are still speculating as to what causes them.
Thanks to subsequent discoveries and research, astronomers now know that FRBs are far more common than previously thought. In fact, according to a new study by a team of researchers from the Harvard-Smithsonian Center for Astrophysics (CfA), FRBs may occur once every second within the observable Universe. If true, FRBs could be a powerful tool for researching the origins and evolution of the cosmos.
As noted, FRBs have remained something of a mystery since they were first discovered. Not only do their causes remain unknown, but much about their true nature is still not understood. As Dr. Fialkov told Universe Today via email:
“FRBs (or fast radio bursts) are astrophysical signals of an undetermined nature. The observed bursts are short (or millisecond duration), bright pulses in the radio part of the electromagnetic spectrum (at GHz frequencies). Only 24 bursts have been observed so far and we still do not know for sure which physical processes trigger them. The most plausible explanation is that they are launched by rotating magnetized neutron stars. However, this theory is to be confirmed.”
For the sake of their study, Fialkov and Loeb relied on observations made by multiple telescopes of the repeating fast radio burst known as FRB 121102. This FRB was first observed in 2012 by researchers using the Arecibo radio telescope in Puerto Rico, and has since been confirmed to be coming from a galaxy located 3 billion light years away in the direction of the Auriga constellation.
Since it was discovered, additional bursts have been detected coming from its location, making FRB 121102 the only known example of a repeating FRB. This repetitive nature has also allowed astronomers to conduct more detailed studies of it than any other FRB. As Prof. Loeb told Universe Today via email, these and other reasons made it an ideal target for their study:
“FRB 121102 is the only FRB for which a host galaxy and a distance were identified. It is also the only repeating FRB source from which we detected hundreds of FRBs by now. The radio spectrum of its FRBs is centered on a characteristic frequency and not covering a very broad band. This has important implications for the detectability of such FRBs, because in order to find them the radio observatory needs to be tuned to their frequency.”
Image of the sky where the radio burst FRB 121102 was found, in the constellation Auriga. You can see its location with a green circle. At left is supernova remnant S147 and at right, a star formation area called IC 410. Credit: Rogelio Bernal Andreo (DeepSkyColors.com)
Based on what is known about FRB 121102, Fialkov and Loeb conducted a series of calculations that assumed that it’s behavior was representative of all FRBs. They then projected how many FRBs would exist across the entire sky and determined that within the observable Universe, a FRB would likely be taking place once every second. As Dr. Fialkov explained:
“Assuming that FRBs are produced by galaxies of a particular type (e.g., similar to FRB 121102) we can calculate how many FRBs have to be produced by each galaxy to explain the existing observations (i.e., 2000 per sky per day). With this number in mind we can infer the production rate for the entire population of galaxies. This calculation shows that an FRB occurs every second when accounting for all the faint events.”
While the exact nature and origins of FRBs are still unknown – suggestions include rotating neutron stars and even alien intelligence! – Fialkov and Loeb indicate that they could be used to study the structure and evolution of the Universe. If indeed they occur with such regular frequency throughout the cosmos, then more distant sources could act as probes which astronomers would then rely on to plumb the depths of space.
For instance, over vast cosmic distances, there is a significant amount of intervening material that makes it difficult for astronomers to study the Cosmic Microwave Background (CMB) – the leftover radiation from the Big Bang. Studies of this intervening material could lead to a new estimates of just how dense space is – i.e. how much of it is composed of ordinary matter, dark matter, and dark energy – and how rapidly it is expanding.
Gemini composite image of the field around FRB 121102, the only repeating FRB discovered so far. Credit: Gemini Observatory/AURA/NSF/NRC
And as Prof. Loeb indicated, FRBs could also be used to explore enduring cosmlogical questions, like how the “Dark Age” of the Universe ended:
“FRBs can be used to measure the column of free electrons towards their source. This can be used to measure the density of ordinary matter between galaxies in the present-day universe. In addition, FRBs at early cosmic times can be used to find out when the ultraviolet light from the first stars broke up the primordial atoms of hydrogen left over from the Big Bang into their constituent electrons and protons.”
The “Dark Age”, which occurred between 380,000 and 150 million years after the Big Bang, was characterized by a “fog” of hydrogen atoms interacting with photons. As a result of this, the radiation of this period is undetectable by our current instruments. At present, scientists are still attempting to resolve how the Universe made the transition between these “Dark Ages” and subsequent epochs when the Universe was filled with light.
This period of “reionization”, which took place 150 million to 1 billion years after the Big Bang, was when the first stars and quasars formed. It is generally believed that UV light from the first stars in the Universe traveled outwards to ionize the hydrogen gas (thus clearing the fog). A recent study also suggested that black holes that existed in the early Universe created the necessary “winds” that allowed this ionizing radiation to escape.
To this end, FRBs could be used to probe into this early period of the Universe and determine what broke down this “fog” and allowed light to escape. Studying very distant FRBs could allow scientists to study where, when and how this process of “reionization” occurred. Looking ahead, Fialkov and Loeb explained how future radio telescopes will be able to discover many FRBs.
The planned Square Kilometer Array will be the world’s largest radio telescope when it begins operations in 2018. Credit: SKA
“Future radio observatories, like the Square Kilometer Array, will be sensitive enough to detect FRBs from the first generation of galaxies at the edge of the observable universe,” said Prof. Loeb. “Our work provides the first estimate of the number and properties of the first flashes of radio waves that lit up in the infant universe.”
And then there’s the Canadian Hydrogen Intensity Mapping Experiment (CHIME) at the at the Dominion Radio Astrophysical Observatory in British Columbia, which recently began operating. These and other instruments will serve as powerful tools for detecting FRBs, which in turn could be used to view previously unseen regions of time and space, and unlock some of the deepest cosmological mysteries.
“[W]e find that a next generation telescope (with a much better sensitivity than the existing ones) is expected to see many more FRBs than what is observed today,” said Dr. Fialkov. “This would allow to characterize the population of FRBs and identify their origin. Understanding the nature of FRBs will be a major breakthrough. Once the properties of these sources are known, FRBs can be used as cosmic beacons to explore the Universe. One application is to study the history of reionization (cosmic phase transition when the inter-galactic gas was ionized by stars).”
It is an inspired thought, using natural cosmic phenomena as research tools. In that respect, using FRBs to probe the most distant objects in space (and as far back in time as we can) is kind of like using quasars as navigational beacons. In the end, advancing our knowledge of the Universe allows us to explore more of it.
View of Mercury's north pole. based on MESSENGER probe data, showing polar deposits of water ice.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/National Astronomy and Ionosphere Center, Arecibo Observatory.
Back in 2012, scientists were delighted to discover that within the polar regions of Mercury, vast amounts of water ice were detected. While the existence of water ice in this permanently-shaded region had been the subject of speculation for about 20 years, it was only after the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft studied the polar region that this was confirmed.
Based on the MESSENGER data, it was estimated that Mercury could have between 100 billion to 1 trillion tons of water ice at both poles, and that the ice could be up to 20 meters (65.5 ft) deep in places. However, a new study by a team of researchers from Brown University indicates that there could be three additional large craters and many more smaller ones in the northern polar region that also contain ice.
Artist’s concept of the MESSENGER spacecraft on approach to Mercury. Credit: NASA/JPL
Despite being the closest planet to the Sun, and experiencing scorching surface temperatures on its Sun-facing side, Mercury’s low axial tilt means that its polar regions are permanently shaded and experience average temperatures of about 200 K (-73 °C; -100 °F). The idea that ice might exist in these regions dates back to the 1990s, when Earth-based radar telescopes detected highly reflective spots within the polar craters.
This was confirmed when the MESSENGER spacecraft detected neutron signals from the planet’s north pole that were consistent with water ice. Since that time, it has been the general consensus that Mercury’s surface ice was confined to seven large craters. But as Ariel Deutsch explained in a Brown University press statement, she and her team sought to look beyond them:
“The assumption has been that surface ice on Mercury exists predominantly in large craters, but we show evidence for these smaller-scale deposits as well. Adding these small-scale deposits to the large deposits within craters adds significantly to the surface ice inventory on Mercury.”
For the sake of this new study, Deutsch was joined by Gregory A. Neumann, a research scientist from NASA’s Goddard Space Flight Center, and James W. Head. In addition to being a professor the Department of Earth, Environmental and Planetary Sciences at Brown, Head was also a co-investigator for the MESSENGER and the Lunar Reconnaissance Orbiter missions.
A view of the crater Prokofiev on Mercury. The crater is the largest one on the planet’s north pole area to have “radar-bright” material, a probable sign of ice. Credit: NASA/JHUAPL/CIW
Together, they examined data from MESSENGER’s Mercury Laser Altimeter (MLA) instrument. This instrument was used by MESSENGER to measure the distance between the spacecraft and Mercury, the resulting data being then used to create detailed topographical maps of the planet’s surface. But in this case, the MLA was used to measure surface reflectance, which indicated the presence of ice.
As an instrument specialist with the MESSENGER mission, Neumann was responsible for calibrating the altimeter’s reflectance signal. These signals can vary based on whether the measurements are taken from overhead or at an angle (the latter of which is refereed to as “off-nadir” readings). Thanks to Neumann’s adjustments, researchers were able to detect high-reflectance deposits in three more large craters that were consistent with water ice.
According to their estimates, these three craters could contain ice sheets that measure about 3,400 square kilometers (1313 mi²). In addition, the team also looked at the terrain surrounding these three large craters. While these areas were not as reflective as the ice sheets inside the craters, they were brighter than the Mercury’s average surface reflectance.
Beyond this, they also looked at altimeter data to seek out evidence of smaller scale deposits. What they found was four smaller craters, each with diameters of less than 5 km (3 mi), which were also more reflective than the surface. From this, they deduced that there were not only more large deposits of ice that were previously undiscovered, but likely many smaller “cold traps” where ice could exist as well.
A forced perspective view of Mercury’s cratered north pole, showing the presence of water ice in yellow. Credit: NASA/JHUAPL/CIW
Between these three newly-discovered large deposits, and what could be hundreds of smaller deposits, the total volume of ice on Mercury could be considerably more than we previously thought. As Deutsch said:
“We suggest that this enhanced reflectance signature is driven by small-scale patches of ice that are spread throughout this terrain. Most of these patches are too small to resolve individually with the altimeter instrument, but collectively they contribute to the overall enhanced reflectance… These four were just the ones we could resolve with the MESSENGER instruments. We think there are probably many, many more of these, ranging in sizes from a kilometer down to a few centimeters.”
In the past, studies of the lunar surface also confirmed the presence of water ice in its cratered polar regions. Further research indicated that outside of the larger craters, small “cold traps”could also contain ice. According to some models, accounting for these smaller deposits could effectively double estimates on the total amounts of ice on the Moon. Much the same could be true for Mercury.
But as Jim Head (who also served as Deutsch Ph.D. advisor for this study) indicated, this work also adds a new take to the critical question of where water in the Solar System came from. “One of the major things we want to understand is how water and other volatiles are distributed through the inner Solar System—including Earth, the Moon and our planetary neighbors,” he said. “This study opens our eyes to new places to look for evidence of water, and suggests there’s a whole lot more of it on Mercury than we thought.”
This shaded relief image shows the Moon’s Shackleton Crater, a 21-km-wide crater permanently shadowed crater near the lunar south pole. The crater’s interior structure is shown in false color based on data from NASA’s LRO probe. Credit: NASA
In addition to indicating the Solar System may be more watery than previously suspected, the presence of abundant ice on Mercury and the Moon has bolstered proposals for building outposts on these bodies. These outposts could be capable of turning local deposits water ice into hydrazine fuel, which would drastically reduce the costs of mounting long-range missions throughout the Solar System.
On the less-speculative side of things, this study also offers new insights into how the Solar System formed and evolved. If water is far more plentiful today than we knew, it would indicate that more was present during the early epochs of planetary formation, presumably when it was being distributed throughout the Solar System by asteroids and comets.
The more that planetary astronomers study asteroids, they more they’re realizing just how varied and different they can be. Some, like 16 Psyche are made of solid nickel and iron, while others are made of rock. Some asteroids have been found with moons, rings, and some icy objects really blur the line between comet and asteroid. In order to truly understand their nature, it would take dozens or maybe hundreds of individual missions on the scale of Rosetta or New Horizons.
Or maybe not. Asteroid 1998 QE2 and its moon
A team of researchers with the Finnish Meteorological Institute announced today that the best way to explore the varied objects in the asteroid belt would be with a fleet of tiny nanosatellites – 50 ought to do the trick to explore 300 separate asteroids, bringing the individual costs down to a few hundred thousand dollars per asteroid. During a presentation they made at the European Planetary Science Congress (EPSC) 2017 in Riga on Tuesday, the researchers showed how these tiny satellites could travel out to the asteroid belt, gather data on individual asteroids, and return to Earth to download their data.
The 50 satellites could be launched together in a single vehicle, and then separate once in space, or they could fill extra space in existing launches. The exact launch orbit doesn’t matter, as long as the spacecraft can get outside the Earth’s protective magnetosphere, where they can catch a ride on the solar wind.
Once in space, 5-kg spacecraft would deploy a 20 km-long wire tether that would catch the solar wind; the constantly flowing particles coming off the Sun, imparting a tiny thrust. This is known as an “E-sail” or electric sail. Unlike a solar sail, which depends on the momentum of photons coming from the Sun, electric sails harvest the momentum of charged protons. Artist’s illustration of the Heliopause Electrostatic Rapid Transit System.
Researchers are still figuring out if this is an effective propulsion system for spacecraft. An Estonian prototype satellite was launched back in 2015, but its onboard motor failed to reel out its tether. The Finnish Aalto-1 satellite launched in June, 2017, and will test out a prototype electric sail in addition to several other experiments over the course of the next year. Even more advanced versions have been proposed, such as Heliopause Electrostatic Rapid Transit System (or HERTS), a mission which could reach 100 astronomical units in 10-15 years by deploying a huge electrified net in space.
In the case of this asteroid mission, each satellite’s electric sail would only give it a change in velocity of only one millimeter per second, but over the course of a 3.2 year mission, it would allow the spacecraft to reach the asteroid belt and return to Earth.
Mission trajectory. The spacecraft would take 3.2 years to reach the asteroid belt and return.In fact, the spacecraft would use their tethers to maneuver within the asteroid belt, flying past as many targets as they can with this minuscule thrust. Each satellite should be able to reach at least 6-7 numbers asteroids, and maybe even more smaller ones.
Each satellite would be equipped with a telescope with only a 40 mm aperture. That’s the size of a small spotting scope or half a pair of binoculars, but it would be enough to resolve features on the surface of an asteroid as large as 100 meters across from 1,000 km away. In addition to taking visual images of the asteroid targets, the spacecraft would be equipped with an infrared spectrometer to determine its meteorology.
Because the spacecraft are so small, they won’t be capable of carrying a transmitter to send their data back to Earth. Instead, they’d store all their scientific findings on a memory card, and then dump their data when their orbit brings them back close to Earth.
The researchers estimate that development of the mission would probably cost about 60 million Euros, or $70 million dollars, bringing the cost per asteroid down to about 200,000 Euros or $240,000.
Between the orbits of Mars and Jupiter lies a disk of rocks, small bodies and planetoids known as the Main Asteroid Belt. The existence of this Belt was first theorized in the 18th century, based on observations that indicated a regular pattern in the orbits of Solar planets. By the following century, regular discoveries began to be made in the space between Mars and Jupiter, prompting astronomers to theorize where the Belt came from.
For a long time, scientists debated whether the Belt was the remains of a planet that broke up, or remnants left over from the early system that failed to become a planet. But a new study by a pair of astronomers from the University of Bordeaux has offered a different take. According to their theory, the Asteroid Belt began as an empty space which was gradually filled by rocks and debris over time.
For the sake of their study – which recently appeared in the journal Science Advances under the title “The Empty Primordial Asteroid Belt” – astronomers Sean N. Raymond and Andre Izidoro of the University of Bordeaux considered the current scientific consensus, which is that the Main Belt was once much more densely packed and became depleted of mass over time.
Artist’s impression of how the Asteroid Belt could have become filled with C-type and S-type asteroids over time. Credit: Sean Raymond/planetplanet.net
As Dr. Raymond explained to Universe Today via email:
“The standard picture is that the building blocks of the Solar System — what we call planetesimals, generally thought of as 10-100 km-scale bodies — started off in a smooth distribution across the Sun’s planet-forming disk. The problem is, that puts a couple of times Earth’s mass in the asteroid belt, where there is now less than a thousandth of an Earth mass. The challenge in this picture is therefore to understand how the belt lost 99.9% of its mass (but not 100%).”
To this, Dr. Raymond and Dr. Izodoro considered the alternate possibility that perhaps the primordial belt started as an empty space. In accordance with this theory, there were no planetesimals – i.e. Ceres, Vesta, Palla, and Hygeia – orbiting between Mars and Jupiter as there are today. This began as a thought experiment which, as Dr. Raymond admits, sounded a bit crazy at first.
However, he and Dr. Izodoro soon realized that several protoplanetary disks like the one they were envisioning had already been discovered in other star systems. For example, in 2014, the Atacama Large Millimeter/submillimeter Array in Chile photographed a planet-forming disk of dust and gas (aka, a protoplanetary disk) in the HL Tauri system, a very young star located about 450 light years away in the Taurus constellation.
As the image (shown below) revealed, the dust in this disk is not smooth, but consists of several broad regions and less dense regions. “The exact explanation for the structure in this disk is still debated but pretty much all models invoke drifting dust,” said Raymond. “And planetesimals form when drifting dust piles up into sufficiently-dense rings. So, dust rings should (we think) produce rings of planetesimals.”
Image of the HL Tau planet-forming disk taken with the Atacama Large Millimeter Array. Credit: ALMA (ESO/NAOJ/NRAO)
To test this hypothesis, they constructed a model of the early Solar System which included an empty Main Belt region. As they moved the simulation forward, they found that the formation of the disk was related to the formation of the rocky planets, and would gradually become what we see today. As Raymond indicated:
“What we found is that the growth of the rocky planets is not 100% efficient. A fraction of planetesimals is gravitationally kicked outward and stranded in the asteroid belt. The orbits of captured bodies matches closely those of S-type asteroids. The efficiency of implanting S-types in the belt is quite low, only about 1 in 1000. However, recall that the belt is almost empty. There is a total of about 4 hundred-thousandths of an Earth-mass in S-types in the present-day belt. Our simulations typically implanted a few times that amount. Given that some are lost during later evolution of the Solar System, this matches both the distribution and amount of S-type asteroids in the belt.
They then combined this model with previous work which looked at the growth of Jupiter and Saturn and how this would effect the Solar System. In this study, they showed the C-type asteroids would be deposited in the Belt over time, and that these asteroids would also be responsible for delivering water to Earth. When they combined the distribution of implanted C-type and S-type asteroids with their current work, they found that it matched the present-day distribution of asteroids.
Interestingly enough, this is not the first theory Raymond and Izodoro have come up with to address the Asteroid Belt’s missing mass. Back in 2011, Raymond was a co-author on the study that proposed the Grand Tack model, in which he and his colleagues proposed that Jupiter migrated from its original orbit after it formed. At first, the planet moved closer to Mars’ current orbit, then back out towards where it is today.
Diagram comparing two possible explanations for how the Asteroid Belt formed. Credit: Sean Raymond/planetplanet.net
In the process, the asteroid belt would have been cleared, and Mars would have been deprived of mass, thus leading to its diminutive size – relative to Earth and Venus. This resolved a key problem with classical theories of Asteroid Belt formation, which was known as the “small Mars problem”. In short, all previous simulations of Solar planet formation tended to produce Mars analogs that were far more massive than Mars is today.
However, the Grand Tack hypothesis still contained theoretical uncertainties, which prompted Raymond and Izodoro to consider the the Empty Primordial Belt theory. “Our new result lends credence to an alternate model in which planetesimals never formed in the asteroid belt at all,” he said. “Different pieces of this new alternative model have been developed in recent years, and I think they add up to make a solid alternative to the Grand Tack model.”
Looking ahead, Raymond says that he and Izodoro hope to conduct further studies and simulations to see if either theory can be confirmed or falsified. “That’s the next step,” he said. “Until the next (seemingly-)crazy idea!”
Artist's impression of Planet Nine, blocking out the Milky Way. The Sun is in the distance, with the orbit of Neptune shown as a ring. Credit: ESO/Tomruen/nagualdesign
In January of 2016, astronomers Mike Brown and Konstantin Batygin published the first evidence that there might be another planet in our Solar System. Known as “Planet 9”, this hypothetical body was believed to orbit at an extreme distance from our Sun. Since that time, multiple studies have been produced that have had tried to address the all-important question of where Planet 9 could have come from.
Whereas some studies have suggested that the planet moved to the edge of the Solar System after forming closer to the Sun, others have suggested that it might be an exoplanet that was captured early in the Solar System’s history. A recent study by a team of astronomers has cast doubt on this latter possibility, however, and indicates that Planet 9 likely formed closer to the Sun and migrated outward during its history.
Their study, titled “Was Planet 9 Captured in the Sun’s Natal Star-Forming Region?“, recently appeared in the Monthly Notices of the Royal Astronomical Society. The team was led by Dr. Richard Parker from the University of Sheffield’s Department of Physics and Astronomy, with colleagues from ETH Zurich. Together, they conducted simulations that cast doubt on the “capture” scenario.
The six most distant known objects in the solar system with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Credit: Caltech/R. Hurt (IPAC); [Diagram created using WorldWide Telescope.]The existence of Planet 9 (or Planet X, for those who maintain that Pluto is still a planet) was first suggested in 2014 by astronomers Chad Trujillo and Scott S. Sheppard, based on the unusual behavior of certain populations of extreme Trans-Neptunian Objects (eTNOs). From a number of studies that took place over the next few years, constraints were gradually placed on the basic parameters of this planet.
Essentially, Planet 9 is believed to be at least ten times as massive as Earth and two to four times the size. It also believed to have a highly elliptical orbit around the Sun, at an average distance (semi-major axis) of approximately 700 AU and ranging from about 200 AU at perihelion to 1200 AU at aphelion. Last, but not least, scientists have estimated that Planet 9 takes between 10,000 and 20,000 years to complete a single orbit of the Sun.
Because of this, it appears unlikely that Planet 9 could have formed in its current location. Hence why astronomers have argued that it either formed closer to the Sun or was captured from another star system billions of years ago. As Dr. Parker explained in University of Sheffield press statement:
“We know that planetary systems form at the same time as stars, and when stars are very young they are usually found in groups where interactions between stellar siblings are common. Therefore, the environment where stars form directly affects planetary systems like our own, and is usually so densely populated that stars can capture other stars or planets.”
Animated diagram showing the spacing of the Solar Systems planet’s, the unusually closely spaced orbits of six of the most distant KBOs, and the possible “Planet 9”. Credit: Caltech/nagualdesign
For the sake of their study, the team conducted simulations of the Solar System when it was still in its “nursery” phase – i.e. in the early process of formation. While interactions with other star systems (and their planets) are known to be common in this period, the team found that even where conditions were optimized for the sake of capturing free-floating planets, the odds of Planet 9 being captured were quite low.
Overall, their simulations indicated that with an orbit like that of Planet 9, only 5 to 10 planets out of 10,000 would be captured when the Solar System was still young. In short, the likelihood that Planet 9 could have been booted out of another star system and captured by our Sun was a paltry 1 out of a 1,000 to 2,000. Not exactly betting odds! As Dr. Parker summarized:
“In this work, we have shown that – although capture is common – ensnaring planets onto the postulated orbit of Planet 9 is very improbable. We’re not ruling out the idea of Planet 9, but instead we’re saying that it must have formed around the sun, rather than captured from another planetary system.”
If Planet 9 was not captured, then there remains only one possibility: ut formed closer to our Sun and gradually migrated beyond the orbit of Neptune, reaching distances occupied only by the most extreme Kuiper Belt Objects. And while the hunt of this elusive and mysterious planet is ongoing, any research which places additional constraints on its characteristics and origin are extremely useful.
By ruling out different scenarios in which the planet formed, researchers are also raising new questions about the history and evolution of our Solar System. From when did all the planets we know come from? Did they form in their current orbits, or did migration play a role? These and other questions are sure to be raised and addressed as we close in on Planet 9.
Illustration showing one of the darkest known exoplanets - a hot Jupiter as black
as fresh asphalt - orbiting a star like our Sun. The day side of the planet, called
WASP-12b, eats light rather than reflects it into space. Something is pulling this planet into its star. Credit: NASA, ESA, and G. Bacon (STScI)
The study of extra-solar planets has revealed discoveries that have confounded expectations and boggled the mind! Whether it’s Super-Earths that become diamond planets, multiple rocky planets orbiting closely together, or “Hot Jupiters” with traces of gaseous metal in their atmospheres, there’s been no shortage of planets out there for which there is no comparison here in the Solar System.
In this respect, WASP-12b is in good company. This Hot-Jupiter, located in a star system 1400 light years from Earth in the direction of the Auriga constellation, was recently studied by a team of astronomers using the Hubble Space Telescope. Due to the particular nature of its atmosphere, which absorbs the vast majority of light it receives instead of reflecting it, this planet appeared pitch black when observed by the Hubble team.
WASP-12b orbits so close to its star that it is heated to a record-breaking 2500°C. Credit: ESA/C Carreau
Like all Hot Jupiters, WASP-12b is similar in mass to Jupiter (1.35 to 1.43 Jupiter masses) and orbits very close to its star. At a distance of just 3.4 million km (2.115 million mi), or 0.0229 AU, it takes a little over a day to complete a single orbit. Because of its proximity, one side of the planet is constantly facing towards it’s sun – i.e. it is tidally locked with its star.
Because of its orbit, temperatures on the day side of the planet are estimated to reach as high as 2811 K (2538 °C; 4600 °F). It is because of these extreme temperatures that most molecules are unable to survive on the day side of the planet, so clouds cannot form to reflect light back into space. As a result, most incoming light penetrates deep into the planet’s atmosphere, where it is absorbed by hydrogen atoms and converted into heat energy.
This was what Bell and his team noticed as they observed the planet passing behind its star (aka. an optical eclipse). Using the STIS, they monitored the system for any dips in starlight, which would indicate how much reflected light was being given off by the planet. However, their observations did not detect reflected light, which indicated that the sun-facing side was absorbing most of the light it was receiving.
As Bell explained in a NASA press statement, this was quite the unusual find: “We did not expect to find such a dark exoplanet,” he said. “Most hot Jupiters reflect about 40 percent of starlight.” However, observations conducted of the night side of the planet show that things are quite different there. On this side, temperatures are about 1366 K (1093 °C; 2000 °F) cooler, which allows water vapor and clouds to form.
An artist’s impression of WASP 12-b being slowly consumed as a result of its ridiculously tight orbit around its star. Credit: NASA.
Back in 2013, scientists working with the HST detected traces of water vapor in the atmosphere (and possible traces of clouds as well) while studying the day/night boundary. As Bell indicated, this new research just goes to show just how diverse this type of gas giant can be:
“This new Hubble research further demonstrates the vast diversity among the strange population of hot Jupiters. You can have planets like WASP-12b that are 4,600 degrees Fahrenheit and some that are 2,200 degrees Fahrenheit, and they’re both called hot Jupiters. Past observations of hot Jupiters indicate that the temperature difference between the day and night sides of the planet increases with hotter day sides. This previous research suggests that more heat is being pumped into the day side of the planet, but the processes, such as winds, that carry the heat to the night side of the planet don’t keep up the pace.”
Since its discovery in 2008, several telescopes have studied WASP-12b, including Hubble, NASA’s Spitzer Space Telescope, and NASA’s Chandra X-ray Observatory. Previous observations by Hubble’s Cosmic Origins Spectrograph (COS) also revealed that the planet may be losing size and mass due to super-heated material from its atmosphere slowly being accreted onto the star.
This is just the latest find in a slew that has confounded scientists expectations about exoplanets. The more we come to learn about the nature and diversity of these distant worlds, the more tantalizing they seem and the more appealing the prospect of exploring them directly someday becomes!
Artist's impression showing the exoplanet WASP-19b, in which atmosphere astronomers detected titanium oxide for the first time. Credit: ESO
The hunt for exoplanets has turned up many fascinating case studies. For example, surveys have turned up many “Hot Jupiters”, gas giants that are similar in size to Jupiter but orbit very close to their suns. This particular type of exoplanet has been a source of interest to astronomers, mainly because their existence challenges conventional thinking about where gas giants can exist in a star system.
Hence why an international team led by researchers from the European Southern Observatory (ESO) used the Very Large Telescope (VLT) to get a better look at WASP-19b, a Hot Jupiter located 815 light-years from Earth. In the course of these observations, they noticed that the planet’s atmosphere contained traces of titanium oxide, making this the first time that this compound has been detected in the atmosphere of a gas giant.
Like all Hot Jupiters, WASP-19b has about the same mass as Jupiter and orbits very close to its sun. In fact, its orbital period is so short – just 19 hours – that temperatures in its atmosphere are estimated to reach as high as 2273 K (2000 °C; 3632 °F). That’s over four times as hot as Venus, where temperatures are hot enough to melt lead! In fact, temperatures on WASP-19b are hot enough to melt silicate minerals and platinum!
The study relied on the FOcal Reducer/low dispersion Spectrograph 2 (FORS2) instrument on the VLT, a multi-mode optical instrument capable of conducting imaging, spectroscopy and the study of polarized light (polarimetry). Using FORS2, the team observing the planet as it passed in front of its star (aka. made a transit), which revealed valuable spectra from its atmosphere.
After carefully analyzing the light that passed through its hazy clouds, the team was surprised to find trace amounts of titanium oxide (as well as sodium and water). As Elyar Sedaghati, who spent 2 years as a student with the ESO to work on this project, said of the discovery in an ES press release:
“Detecting such molecules is, however, no simple feat. Not only do we need data of exceptional quality, but we also need to perform a sophisticated analysis. We used an algorithm that explores many millions of spectra spanning a wide range of chemical compositions, temperatures, and cloud or haze properties in order to draw our conclusions.”
Titanium oxide is a very rare compound which is known to exist in the atmospheres of cool stars. In small quantities, it acts as a heat absorber, and is therefore likely to be partly responsible for WASP-19b experiencing such high temperatures. In large enough quantities, it can prevent heat from entering or escaping an atmosphere, causing what is known as thermal inversion.
This is a phenomena where temperatures are higher in the upper atmosphere and lower further down. On Earth, ozone plays a similar role, causing an inversion of temperatures in the stratosphere. But on gas giants, this is the opposite of what usually happens. Whereas Jupiter, Saturn, Uranus and Neptune experience colder temperatures in their upper atmospheres, temperatures are much hotter closer to the core due to increases in pressure.
The team believes that the presence of this compound could have a substantial effect on the atmosphere’s temperature, structure and circulation. What’s more, the fact that the team was able to detect this compound (a first for exoplanet researchers) is an indication of how exoplanet studies are achieving new levels of detail. All of this is likely to have a profound impact on future studies of exoplanet atmospheres.
The study would also have not been possible were it not for the FORS2 instrument, which was added to the VLT array in recent years. As Henri Boffin, the instrument scientist who led the refurbishment project, commented:
“This important discovery is the outcome of a refurbishment of the FORS2 instrument that was done exactly for this purpose. Since then, FORS2 has become the best instrument to perform this kind of study from the ground.”
Looking ahead, it is clear that the detection of metal oxides and other similar substances in exoplanet atmospheres will also allow for the creation of better atmospheric models. With these in hand, astronomers will be able to conduct far more detailed and accurate studies on exoplanet atmospheres, which will allow them to gauge with greater certainty whether or not any of them are habitable.
So while this latest planet has no chance of supporting life – you’d have better luck finding ice cubes in the Gobi desert! – its discovery could help point the way towards habitable exoplanets in the future. On step closer to finding a world that could support life, or possibly that elusive Earth 2.0!
