When ‘Oumuamua crossed Earth’s orbit on October 19th, 2017, it became the first interstellar object to ever be observed by humans. These and subsequent observations – rather than dispelling the mystery of ‘Oumuamua’s true nature – only deepened it. While the debate raged about whether it was an asteroid or a comet, with some even suggesting it could be an extra-terrestrial solar sail.
In the end, all that could be said definitively was that ‘Oumuamua was an interstellar object the likes of which astronomers had never before seen. In their most recent study on the subject, Harvard astronomers Amir Siraj and Abraham Loeb argue that such objects may have impacted on the lunar surface over the course of billions of years, which could provide an opportunity to study these objects more closely.
The ESA has announced a new mission to explore a comet. The Comet Interceptor mission will have a spacecraft wait in space until a pristine comet approaches the inner Solar System. Then it will make a bee line for it, and do some ground-breaking science.
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.