When ‘Oumuamua was first detected on October 19th, 2017, astronomers were understandably confused about the nature of this strange object. Initially thought to be an interstellar comet, it was then designated as an interstellar asteroid. But when it picked up velocity as it departed our Solar System (a very comet-like thing to do), scientists could only scratch their heads and wonder.
After much consideration, Shmuel Bialy and Professor Abraham Loeb of the Harvard-Smithsonian Center for Astrophysics (CfA) proposed that ‘Oumuamua could in fact be an artificial object (possibly an alien probe). In a more recent study, Amir Siraj and Prof. Loeb identified another (and much smaller) potential interstellar object, which they claim could be regularly colliding with Earth.
During the 1940s, Hungarian-American scientist John von Neumann developed a mathematical theory for how machines could endlessly reproduce themselves. This work gave rise to the idea of “von Neumann probes“, a class of self-replicating interstellar probes (SRPs) that could be used to do everything from exploring the Universe to seeding it with life and intervening in species evolution.
Some have naturally suggested that this be a focus SETI research, which would entail looking for signs of self-replicating spacecraft in our galaxy. But as is always the case with proposals like these, the Fermi Paradox eventually reasserts itself by asking the age-old question – “Where is everybody?” If there are alien civilizations out there, why haven’t we found any evidence of their SRPs?
Since it was first detected hurling through our Solar System, the interstellar object known as ‘Oumuamua has been a source of immense scientific interest. Aside from being extrasolar in origin, the fact that it has managed to defy classification time and again has led to some pretty interesting theories. While some have suggested that it is a comet or an asteroid, there has even been the suggestion that it might be an interstellar spacecraft.
However, a recent study may offer a synthesis to all the conflicting data and finally reveal the true nature of ‘Oumuamua. The study comes from famed astronomer Dr. Zdenek Sekanina of the NASA Jet Propulsion Laboratory, who suggests that ‘Oumuamua is the remnant of an interstellar comet that shattered before making its closest pass to the Sun (perihelion), leaving behind a cigar-shaped rocky fragment.
Rather than resolving the dispute, additional observations only deepened the mystery, even giving rise to suggestions that it might be an extra-terrestrial solar sail. For this reason, scientists are very interested in finding other examples of ‘Oumuamua-like objects. According to a recent study by a team of Harvard astrophysicists, it is possible that interstellar objects enter our system and end up falling into in our Sun somewhat regularly.
On October 19th, 2017, the first interstellar object – named 1I/2017 U1 (aka. ‘Oumuamua) – to be observed in our Solar System was detected. In the months that followed, multiple follow-up observations were conducted to gather more data on its composition, shape, and possible origins. Rather than dispel the mystery surrounding the true nature of ‘Oumuamua – is a comet or an asteroid? – these efforts have only managed to deepen it.
In a recent study, Harvard Professor Abraham Loeb and Shmuel Bialy – a postdoctoral researcher from the Smithsonian Center for Astrophysics (CfA) – addressed this mystery by suggesting that ‘Oumuamua may be an extra-terrestrial solar sail. Building on this, Loeb and Amir Siraj (a Harvard undergraduate student) conducted a new study that indicated that hundreds of “‘Oumuamua-like” objects could be detectable in our Solar System.
Interestingly enough, there has also been some speculation that based on its shape, ‘Oumuamua might actually be an interstellar spacecraft (Breakthrough Listen even monitored it for signs of radio signals!). A new study by a pair of astronomers from the Harvard Smithsonian Center for Astrophysics (CfA) has taken it a step further, suggesting that ‘Oumuamua may actually be a light sail of extra-terrestrial origin.
In all this time, the question of ‘Oumuamua’s origin has remained unanswered. Beyond theorizing that it came from the direction of the Lyra Constellation, possibly from the Vega system, there have been no definitive answers. Luckily, an international team led by researchers from the Max Planck Institute for Astronomy (MPIA) have tracked ‘Oumuamua and narrowed down its point of origin to four possible star systems.
Since that time, multiple studies have been conducted to learn more about this interstellar visitor, and some missions have even been proposed to go and study it up close. However, the most recent study of ‘Oumuamua, conducted by a team of international scientists, has determined that based on the way it left our Solar System, ‘Oumuamua is likely to be a comet after all.
As noted, when it was first discovered – roughly a month after it made its closest approach to the Sun – scientists believed ‘Oumuamua was an interstellar comet. However, follow-up observations showed no evidence of gaseous emissions or a dusty environment around the body (i.e. a comet tail), thus leading to it being classified as a rocky interstellar asteroid.
This was followed by a team of international researchers conducting a study that showed how ‘Oumuamua was more icy that previously thought. Using the ESO’s Very Large Telescope in Chile and the William Herschel Telescope in La Palma, the team was able to obtain spectra from sunlight reflected off of ‘Oumuamua within 48 hours of the discovery. This revealed vital information about the composition of the object, and pointed towards it being icy rather than rocky.
The presence of an outer-layer of carbon rich material also explained why it did not experience outgassing as it neared the Sun. Following these initial observations, Marco Micheli and his team continued to conduct high-precision measurements of ‘Oumuamua and its position using ground-based facilities and the NASA/ESA Hubble Space Telescope.
By January, Hubble was able to snap some final images before the object became too faint to observe as it sped away from the Sun on its way to leaving the Solar System. To their surprise, they noted that the object was increasing its velocity deviating from the trajectory it would be following if only the gravity of the Sun and the planets were influencing its course.
In short, they discovered that ‘Oumuamua was not slowing down as expected, and as of June 1st, 2018, was traveling at a speed of roughly 114,000 km/h (70,800 mph). The most likely explanation, according to the team, is that ‘Oumuamua is venting material from its surface due to solar heating (aka. outgassing). The release of this material would give ‘Oumuamua the steady push it needed to achieve this velocity.
As Davide Farnocchia, a researcher from NASA’s Jet Propulsion Laboratory and a co-author on the paper, explained in a recent ESA press release:
“We tested many possible alternatives and the most plausible one is that ’Oumuamua must be a comet, and that gasses emanating from its surface were causing the tiny variations in its trajectory.”
Moreover, the release of gas pressure would also explain how ‘Oumuamua is veering off course since outgassing has been known to have the effect of perturbing the comet’s path. Naturally, there are still some mysteries that still need to be solved about this body. For one, the team still has not detected any dusty material or chemical signatures that typically characterize a comet.
As such, the team concluded that ‘Oumuamua must have been releasing only a very small amount of dust, or perhaps was releasing more pure gas without much dust. In either case, ‘Oumuamua is estimated to be a very small object, measuring about 400 meters (1312 ft) long. In the end, the hypothesized outgassing of ‘Oumuamua remains a mystery, much like its origin.
In fact, the team originally performed the Hubble observations on ‘Oumuamua in the hopes of determining its exact path, which they would then use to trace the object back to its parent star system. These new results mean this will be more challenging than originally thought. As Olivier Hainaut, a researcher from the European Southern Observatory and a co-author on the study, explained:
“It was extremely surprising that `Oumuamua first appeared as an asteroid, given that we expect interstellar comets should be far more abundant, so we have at least solved that particular puzzle. It is still a tiny and weird object, but our results certainly lean towards it being a comet and not an asteroid after all.”
Detlef Koschny, another co-author on the study, is responsible for Near-Earth Object activities under ESA’s Space Situational Awareness program. As he explained, the study of ‘Oumuamua has provided astronomers with the opportunity to improve asteroid detection methods, which could play a vital role in the study of Near-Earth Asteroids and determining if they post a risk.
“Interstellar visitors like these are scientifically fascinating, but extremely rare,” he said. “Near-Earth objects originating from within our Solar System are much more common and because these could pose an impact risk, we are working to improve our ability to scan the sky every night with telescopes such as our Optical Ground Station that contributed to this fascinating discovery.”
Since ‘Oumuamua’s arrival, scientists have determined that there may be thousands of interstellar asteroids currently in our Solar System, the largest of which would be tens of km in radius. Similarly, another study was conducted that revealed the presence of an interstellar asteroid (2015 BZ509) that – unlike ‘Oumuamua, which was an interloper to out system – was captured by Jupiter’s gravity and has since remained in a stable orbit.
This latest study is also timely given the fact that June 30th is global “Asteroid Day”, an annual event designed to raise awareness about asteroids and what can be done to protect Earth from a possible impact. In honor of this event, the ESA co-hosted a live webcast with the European Southern Observatory to discuss the latest science news and research on asteroids. To watch a replay of the webcast, go to the ESA’s Asteroid Day webpage.
News of this interstellar asteroids, the first to ever be detected by astronomers, raised a lot of excitement. And according to a new study by an international pair of astronomers, ‘Oumuamua was not the Solar System’s first interstellar visitor. Whereas ‘Oumuamua was an interloper on its way to another star system, this latest object – known as Asteroid (514107) 2015 BZ509 – appears to be a long-term resident.
After locating this asteroid, the team noticed something very interesting about it. All planets in our Solar System, and the vast majority of objects as well, orbit the Sun in the same direction. However, upon observing 2015 BZ509, the team concluded that it had a retrograde orbit – i.e. it rotated in the opposite direction as the other planets and objects. As Dr. Fathi Namouni, the lead author of the study, explained:
“How the asteroid came to move in this way while sharing Jupiter’s orbit has until now been a mystery. If 2015 BZ509 were a native of our system, it should have had the same original direction as all of the other planets and asteroids, inherited from the cloud of gas and dust that formed them.”
Using a high-resolution statistical search for stable orbits, the team found that 2015 BZ509 has been in its current orbital state since the formation of the Solar System – ca. 4.5 billion years ago. From this, they determined that the asteroid could not be indigenous to the Solar System since it would not have been able to assume its current large-inclination orbit – not when the nearby planets had early coplanar orbits and interacted with coplanar debris.
The only conclusion they could reach from these results was that this asteroid was captured from the interstellar medium 4.5 billion years ago. As Dr. Maria Helena Moreira Morais, the second author on the paper, added:
“Asteroid immigration from other star systems occurs because the Sun initially formed in a tightly-packed star cluster, where every star had its own system of planets and asteroids. The close proximity of the stars, aided by the gravitational forces of the planets, help these systems attract, remove and capture asteroids from one another.”
The discovery of the first interstellar asteroid was certainly excited and led to multiple proposals for sending a mission to study it up close. The discovery of an interstellar asteroid that became a permanent resident in our system, however, has important implications for the study of planet formation, the evolution of the Solar System, and maybe even the origin of life itself – all of which remain open questions at this point.
Looking ahead, Dr. Namouni and Dr. Moraiswant hope to obtain more information on 2015 BZ509 so they might be able to determine exactly when it how it settled in the Solar System. In so doing, they will be able to provide clues about the Sun’s original star nursery, and about how our Early Solar System might have been enriched with components necessary for the appearance of life on Earth.
And who knows? We may soon discovery many more asteroid interlopers and long-term residents in the future. The study of these could provide even more information on the early history of our Solar System, how it interacted with neighboring systems, and how the basic ingredients for life (as we know it) came to be distributed. Perhaps the Rama enthusiasts had a point when they reminded us that the Ramans “do everything in threes”!
In fact, the question of this interstellar object’s origins has been mystery since it was first discovered. While astronomers are sure that it came from the direction of Vega and some details have been learned about its past, where it originated from remains unknown. But according to a new study by a team of astronomers from the University of Toronto, Scarborough, ‘Oumuamua may have originally come from a binary star system.
For the sake of their study, Jackson and his co-authors considered how in single star systems (like our own), asteroids do not get ejected very often. For the most part, it is comets that become interstellar objects, mainly because they orbit the Sun at a greater distance and are less tightly bound by its gravity. And while ‘Oumuamua was initially mistaken for a comet, follow-up observations by the European Southern Observatory (ESO) indicated that it is likely an asteroid.
With the help of other astronomers, it soon became apparent that ‘Oumuamua was likely an oddly-shaped rocky object that measured about 400 meters (1312 ft) long and was tube-shaped. These findings were rather surprising to astronomers. As Jackson explained in a recent Royal Astronomical Society press release:
“It’s really odd that the first object we would see from outside our system would be an asteroid, because a comet would be a lot easier to spot and the Solar System ejects many more comets than asteroids.”
As such, Jackson and his team hypothesized that interstellar objects like ‘Oumuamau are more likely to be ejected from a binary system. To test this theory, they constructed a population synthesis model that considered just how common binary star systems are in the Galaxy. They also conducted 2000 N-body simulations to see just how efficient such systems would be at ejecting objects like ‘Oumuamua.
What they found was that binary stars are produced at a rate of about 30% by number and 41% by mass, and that rocky objects like ‘Oumuamua are far more likely to be ejected from binary than single star systems. Based on ‘Oumuamua’s rocky composition, they also determined that the asteroid was likely ejected from the inner part of its solar system (i.e. inside the “Ice Line”) while the system was still in the process of formation.
Lastly, they determined that rocky objects are ejected from binary systems in comparable numbers to icy objects. This is based on the fact that the presence of a companion star would mean that more material would become unstable due to stellar encounters. In the end, this material would be more likely to be ejected rather than accreted to form planets, or take up residence in the outer reaches of the star system.
While there are still many unanswered questions about ‘Oumuamua, it remains the first interstellar asteroid that scientists have ever known. As such, its continued study can tell us a great deal about what lies beyond our Solar System. As Jackson put it:
“The same way we use comets to better understand planet formation in our own Solar System, maybe this curious object can tell us more about how planets form in other systems.”