Lava flows in Mars' Elysium Planitia region have left a rather good likeness of a woolly mammoth or elephant. The region is known for some of the planet's youngest lavas - this one may formed in the past 100 million years.
Billions of years ago, Mars was a much different place than it is today. Its atmosphere was thicker and warmer, liquid water flowed on its surface, and the planet was geologically active. Due to its lower gravity, this activity led to the largest volcanoes in the Solar System (Olympus Mons and the Thetis Mons region) and the longest, deepest canyon in the world (Valles Marineris). Unfortunately, Mars’ interior began to cool rapidly, its inner core solidified, and geological activity largely stopped. For some time, geologists have believed that Mars was essentially “dead” in the geological sense.
However, recent studies have provided seismic and geophysical evidence that Mars may still be “slightly alive.” In a recent study, scientists from the University of Arizona (ASU) challenged conventional views of Martian geodynamic evolution by discovering evidence of an active mantle plume pushing its way through the crust, causing earthquakes and volcanic eruptions. Combined with some serious marsquakes recorded by NASA’s InSight lander, these finding suggests that there is still some powerful volcanic action beneath the surface of Mars.
Mining asteroids might be necessary for humanity to expand into the Solar System. But what effect would asteroid mining have on the world's economy? Credit: ESA.
In April of 2016, astronomers became aware of a distant object that appeared to be orbiting the Sun, but was also passing close enough to Earth that it could be periodically viewed using the most powerful telescopes. Since then, there has been ample speculation as to what this “Temporary Moon” could be, with most astronomers claiming that it is likely nothing more than an asteroid.
However, some suggested that it was a burnt-out rocket booster trapped in a near-Earth orbit. But thanks to new study by a team from the University of Arizona’s Lunar and Planetary Laboratory, this object – known as (469219) 2016 HO3 – has been confirmed as an asteroid. While this small near-Earth-asteroid orbits the Sun, it also orbits Earth as a sort of “quasi-satellite”.
The team that made this discovery was led by Vishnu Reddy, an assistant professor at the University of Arizona’s Lunar and Planetary Laboratory. Their research was also made possible thanks to NASA’s Near-Earth Object Observations Program. This program is maintained by NASA’s Center for Near-Earth Object Studies (CNEOS) and provides grants to institutions dedicated to the research of NEOs.
2016 HO3 is an asteroid that appears to orbit around Earth due to the mechanics of its peculiar orbit around the sun. Credit: NASA-JPL
The details of this discovery were presented this week at the 49th Annual Meeting of the Division for Planetary Sciences in Utah at a presentation titled “Ground-based Characterization of Earth Quasi Satellite (469219) 2016 HO3”. During the course of the presentation, Reddy and his colleagues described how they spotted the object using the Large Binocular Telescope (LBT) at the LBT Observatory on Mount Graham in southeastern Arizona.
According to their observations, 2016 HO3 measures just 100 meters (330 feet) across and is the most stable quasi-satellite discovered to date (of which there have been five). Over the course of a few centuries, this asteroid remains at a distance of 38 to 100 lunar distances – i.e. the distance between the Earth and the Moon. As Reddy explained in a UANews press statement, this makes the asteroid a challenging target:
“While HO3 is close to the Earth, its small size – possibly not larger than 100 feet – makes it challenging target to study. Our observations show that HO3 rotates once every 28 minutes and is made of materials similar to asteroids.”
Discovering the true nature of this object has also solved another big question – namely, where did 2016 HO3 come from? For those speculating that it might be space junk, it then became necessary to determine what the likely source of that junk was. Was it a remnant of an Apollo-era mission, or something else entirely? By determining that it is actually an NEO, Reddy and his team have indicted that it likely comes from the same place as other NEOs.
Vishnu Reddy of the University of Arizona’s Lunar Planetary Laboratory. Credit: Bob Demers/UANews
Reddy and his colleagues also indicated that 2016 HO3 reflected light off its surface in a way that is similar to meteorites that have been studied here on Earth. This was another indication that 2016 HO3 has similar origins to other NEOs (some of which have entered our atmosphere as meteors) which are generally asteroids that were kicked out of the Main Belt by Jupiter’s gravity.
“In an effort to constrain its rotation period and surface composition, we observed 2016 HO3 on April 14 and 18 with the Large Binocular Telescope and the Discovery Channel Telescope,” Reddy said. “The derived rotation period and the spectrum of emitted light are not uncommon among small NEOs, suggesting that 2016 HO3 is a natural object of similar provenance to other small NEOs.”
But unlike other NEOs which periodically cross Earth’s orbit, “quasi-satellites” are distinguished by their rather unique orbits. In the case of 2016 HO3, it has an orbit that follows a similar path to that the Earth’s; but because it is not dominated by the Earth’s gravity, their two orbits are out of sync. This causes 2016 HO3 to make annual loops around the Earth as it orbits the Sun.
Artist’s impression of a hypothetical astronaut mission to an asteroid. Credit: NASA Human Exploration Framework Team
Christian Veillet, one of co-authors of the presentation, is also the director of the LBT Observatory. As he explained, this characteristic could make “quasi-satellites” ideal targets for future NEO studies:
“Of the near-Earth objects we know of, these types of objects would be the easiest to reach, so they could potentially make suitable targets for exploration. With its binocular arrangement of two 8.4-meter mirrors, coupled with a very efficient pair of imagers and spectrographs like MODS, LBT is ideally suited to the characterization of these Earth’s companions.”
Similarly, their orbital characteristic could make “quasi-satellites” an ideal target for future space missions. One of NASA’s main goals in the coming decade is to send a crewed mission to a Near-Earth Object in order to test the Orion spacecraft and the Space Launch System. Such a mission would also help develop the necessary expertise for mounting missions deeper into space (i.e. to Mars and beyond).
The study of Near-Earth Objects is also of immense importance when it comes to determining how and where as asteroid might pose a threat to Earth. This knowledge allows for advanced warnings which can potentially save lives. It is also significant when it comes to the development of proposed counter-measures, several of which are currently being explored.
And be sure to enjoy this video of 2016 HO3’s orbit, courtesy of NASA’s Jet Propulsion Laboratory:
Artist's concept of the hypothetical "Planet Nine." Could it have moons? Credit: NASA/JPL-Caltech/Robert Hurt
Ever since its existence was first proposed, the evidence for Planet 9 continues to mount. But of course, said evidence has been entirely indirect, consisting mostly of studies that show how the orbits of Trans-Neptunian Objects (TNOs) are consistent with a large object crossing their path. However, evidence is also emerging that comes from the center of the Solar System itself.
This latest line of evidence comes from Caltech, where researchers Elizabeth Bailey, Konstantin Batygin, and Michael E. Brown (the latter of whom were the ones who first proposed Planet 9’s existence) have published a new study linking solar obliquity to the existence of Planet 9. Essentially, they claim that the axial tilt of the Sun (6°) could be due to the gravitational influence a large planet with an extreme orbit.
To recap, the issue of Planet was first raised in 2014 by astronomers Scott Sheppard and Chadwick Trujillo. Noting the similarities in the orbits of distant Trans-Neptunian Objects (TNOs), they postulated that a massive object was likely influencing them. This was followed in 2016 by Konstantin Batygin and Michael E. Brown of Caltech suggesting that an undiscovered planet was the culprit.
The orbits of several KBOs provide indications about the possible existence of Planet 9. Credit: Caltech/R. Hurt (IPAC)
Calling this body Planet 9, they speculated that it had a mass 10 times greater than that of Earth, and took 20,000 years to complete a single orbit of our Sun. They also speculated that its orbit was tilted relative to the other planets of our Solar System, and extremely eccentric. And little by little, examinations of other Solar bodies have shown that Planet 9 is likely out there.
For the sake of their study – “Solar Obliquity Induced by Planet Nine“, which was recently published in the Astrophysical Journal – the research team (led by Bailey) looked to the obliquity of the Sun. As they state in their paper, the six-degree axial tilt of the Sun can only be explained in one of two ways – either as a result of an asymmetry that was present during the formation of Solar System, or because of an external source of gravity.
To test this hypothesis, Bailey, Batygin and Brown used an analytic model to test how interactions between Planet 9 and the rest of the Solar System would effect their orbits over the course of the last 4.5 billion years. As Elizabeth Bailey, a graduate student at Caltech’s Division of Geological and Planetary Sciences and the lead author on the paper, told Universe Today via email:
“We simulated the solar system’s motion. Planet 9 forces the solar system to slowly wobble. If Planet 9 is out there, we are in the process of wobbling right now, as we speak! But it happens very slowly, a few degrees tilt per billion years. Meanwhile the sun is not wobbling much, so it looks like the sun is tilted. A range of Planet 9 parameters cause exactly the configuration of the sun that we see today.
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
In the end, they concluded that the Sun’s obliquity could only be explained by the influence of giant planet with an extreme orbit, one that is consistent with the characteristics attributed to Planet 9. In other words, the existence of Planet 9 offers an explanation for the Sun’s peculiar behavior, something which has remained a mystery until now.
“Planet Nine was first hypothesized because the orbits of objects in the outer reaches of the solar system are confined in physical space,” said Bailey. “Those orbits would be all over the place unless something is currently stopping them. The only explanation so far is Planet Nine. For over 150 years, people have wondered why the sun is tilted. Personally I’d say that Planet 9 offers the first satisfying explanation. If it exists, it tilted the sun.”
The Arizona research team was led by Renu Malhotra, a Regents’ Professor of Planetary Sciences in the University of Arizona’s Lunar and Planetary Lab. For the sake of their study, titled “Corralling a Distant Planet with Extreme Resonant Kuiper Belt Objects“, they examined the orbital patterns of four extreme Kuiper Belt Objects (KBOs), which have the longest orbital periods of any known objects.
Artist’s impression of the the possible Planet 9 at the edge of the Solar System. Credit: Robin Dienel/Carnegie Science
According to their calculations, the presence of a massive planet – one that would complete an orbit around the Sun every 17,117 years, and at an average distance (semimajor axis) of 665 AU – would explain the orbital pattern of these four objects. These results were consistent with the estimates concerning the orbital period of Planet 9, its orbital path, and it mass.
“We analyzed the data of these most distant Kuiper Belt objects,” Malhotra said, “and noticed something peculiar, suggesting they were in some kind of resonances with an unseen planet… Our paper provides more specific estimates for the mass and orbit that this planet would have, and, more importantly, constraints on its current position within its orbit.”
Looks like Planet 9’s days of hiding in the outer Solar System may be numbered!
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
On January 20th, 2016, researchers Konstantin Batygin and Michael E. Brown of Caltech announced that they had found evidence that hinted at the existence of a massive planet at the edge of the Solar System. Based on mathematical modeling and computer simulations, they predicted that this planet would be a super-Earth, two to four times Earth’s size and 10 times as massive. They also estimated that, given its distance and highly elliptical orbit, it would take 10,000 – 20,000 years to orbit the Sun.
Since that time, many researchers have responded with their own studies about the possible existence of this mysterious “Planet 9”. One of the latest comes from the University of Arizona, where a research team from the Lunar and Planetary Laboratory have indicated that the extreme eccentricity of distant Kuiper Belt Objects (KBOs) might indicate that they crossed paths with a massive planet in the past.
For some time now, it has been understood that there are a few known KBOs who’s dynamics are different than those of other belt objects. Whereas most are significantly controlled by the gravity of the gas giants planets in their current orbits (particularly Neptune), certain members of the scattered disk population of the Kuiper Belt have unusually closely-spaced orbits.
The orbits of Neptune (magenta), Sedna (dark magenta), a series of Kuiper belt objects (cyan), and the hypothetical Planet 9 (orange). Credit: Caltech/R. Hurt (IPAC)
When Batygin and Brown first announced their findings back in January, they indicated that these objects instead appeared to be highly clustered with respect to their perihelion positions and orbital planes. What’s more, their calculation showed that the odds of this being a chance occurrence were extremely low (they calculated a probability of 0.007%).
Instead, they theorized that it was a distant eccentric planet that was responsible for maintaining the orbits of these KBOs. In order to do this, the planet in question would have to be over ten times as massive as Earth, and have an orbit that lay roughly on the same plane (but with a perihelion oriented 180° away from those of the KBOs).
Such a planet not only offered an explanation for the presence of high-perihelion Sedna-like objects – i.e. planetoids that have extremely eccentric orbits around the Sun. It would also help to explain where distant and highly inclined objects in the outer Solar System come from, since their origins have been unclear up until this point.
In a paper titled “Coralling a distant planet with extreme resonant Kuiper belt objects“, the University of Arizona research team – which included Professor Renu Malhotra, Dr. Kathryn Volk, and Xianyu Wang – looked at things from another angle. If in fact Planet 9 were crossing paths with certain high-eccentricity KBOs, they reasoned, it was a good bet that its orbit was in resonance with these objects.
Pluto and its cohorts in the icy-asteroid-rich Kuiper Belt beyond the orbit of Neptune. Credit: NASA
To break it down, small bodies are ejected from the Solar System all the time due to encounters with larger objects that perturb their orbits. In order to avoid being ejected, smaller bodies need to be protected by orbital resonances. While the smaller and larger objects may pass within each others’ orbital path, they are never close enough that they would able to exert a significant influence on each other.
This is how Pluto has remained a part of the Solar System, despite having an eccentric orbit that periodically cross Neptune’s path. Though Neptune and Pluto cross each others orbit, they are never close enough to each other that Neptune’s influence would force Pluto out of our Solar System. Using this same reasoning, they hypothesized that the KBOs examined by Batygin and Brown might be in an orbital resonance with the Planet 9.
As Dr. Malhotra, Volk and Wang told Universe Today via email:
“The extreme Kuiper belt objects we investigate in our paper are distinct from the others because they all have very distant, very elliptical orbits, but their closest approach to the Sun isn’t really close enough for them to meaningfully interact with Neptune. So we have these six observed objects whose orbits are currently fairly unaffected by the known planets in our Solar System. But if there’s another, as yet unobserved planet located a few hundred AU from the Sun, these six objects would be affected by that planet.”
After examining the orbital periods of these six KBOs – Sedna, 2010 GB174, 2004 VN112, 2012 VP113, and 2013 GP136 – they concluded that a hypothetical planet with an orbital period of about 17,117 years (or a semimajor axis of about 665 AU), would have the necessary period ratios with these four objects. This would fall within the parameters estimated by Batygin and Brown for the planet’s orbital period (10,000 – 20,000 years).
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
Their analysis also offered suggestions as to what kind of resonance the planet has with the KBOs in question. Whereas Sedna’s orbital period would have a 3:2 resonance with the planet, 2010 GB174 would be in a 5:2 resonance, 2994 VN112 in a 3:1, 2004 VP113 in 4:1, and 2013 GP136 in 9:1. These sort of resonances are simply not likely without the presence of a larger planet.
“For a resonance to be dynamically meaningful in the outer Solar System, you need one of the objects to have enough mass to have a reasonably strong gravitational effect on the other,” said the research team. “The extreme Kuiper belt objects aren’t really massive enough to be in resonances with each other, but the fact that their orbital periods fall along simple ratios might mean that they each are in resonance with a massive, unseen object.”
But what is perhaps most exciting is that their findings could help to narrow the range of Planet 9’s possible location. Since each orbital resonance provides a geometric relationship between the bodies involved, the resonant configurations of these KBOs can help point astronomers to the right spot in our Solar System to find it.
But of course, Malhotra and her colleagues freely admit that several unknowns remain, and further observation and study is necessary before Planet 9 can be confirmed:
“There are a lot of uncertainties here. The orbits of these extreme Kuiper belt objects are not very well known because they move very slowly on the sky and we’ve only observed very small portions of their orbital motion. So their orbital periods might differ from the current estimates, which could make some of them not resonant with the hypothetical planet. It could also just be chance that the orbital periods of the objects are related; we haven’t observed very many of these types of objects, so we have a limited set of data to work with.”
Estimates of Planet Nine’s “possible” and “probable” zones. by French scientists based on a careful study of Saturn’s orbit and using mathematical models. Source: CNRS, Cote d’Azur and Paris observatories. Credit: Bob King
Ultimately, astronomers and the rest of us will simply have to wait on further observations and calculations. But in the meantime, I think we can all agree that the possibility of a 9th Planet is certainly an intriguing one! For those who grew up thinking that the Solar System had nine planets, these past few years (where Pluto was demoted and that number fell to eight) have been hard to swallow.
But with the possible confirmation of this Super-Earth at the outer edge of the Solar System, that number could be pushed back up to nine soon enough!
