22 minutes | Feb 3, 2018

Ep 002 An Interstellar Visitor

Episode 002:  An Interstellar Visitor Hello and welcome, I’m Dr. Andrew J. Wagers - but you can call me Andy.  Join me as we discover that the cosmos doesn't just have a purpose, it has a storyline.  I have saved you a seat, so sit down as the house lights dim in the Theatre of the Cosmos. *************************************************************************** An Interstellar Visitor   By Original: ESO/M. KornmesserDerivative: nagualdesign [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons   Recently, you may have heard the announcement of an exciting discovery, astronomers claim to have found an asteroid from outside our solar system.  1I/2017 U1, or `Oumuamua (pronounced ‘oh-oo-moo-ah-moo-a’) was discovered on Oct. 19th of this year by the Pan-STARRS1 program at the University of Hawaii.  Pan-STARRS stands for, Panoramic Survey Telescope and Rapid Response System and it was designed to detect near Earth asteroids and other transient cellestial objects.  The Pan-STARRS1 team gave it the name `Oumuamua (pronounced ‘oh-oo-moo-ah-moo-a’) which means in Hawaiian, “a messenger from afar who arrives first” (according to NASA) or “messenger from the distant past” (according to Discover Magazine).  Google translate translated the name as “First” for me. The existence of such objects has been proposed since at least the 1970's but this is the first one that has been found.  It was expected that such an object would more likely be a comet rather than an asteroid so there have been some suprises with this discovery.  Today, I want to look at the interesting properties of `Oumuamua (pronounced ‘oh-oo-moo-ah-moo-a’) and investigate the claims that it is an interstellar object. The Facts Here are some things we know about `Oumuamua (pronounced ‘oh-oo-moo-ah-moo-a’), these have been gleaned primarily from the NASA FAQ and articles on arxiv.org: Astronomers can see from the way the brightness of the light varies over time, known as a “light curve”, that the asteroid has rotation period of 7-8 hours.  [Rotation period estimates are inconsistent and varied, with reported values between 6.9 and 8.3 hours. – https://arxiv.org/abs/1711.11530] The light curve also suggests a narrow tubular shaped object.  Initially it was reported to have a ratio 10:1 but more recent data suggest it is closer to 5:1 or 6:1.  Either way, we have never seen anything over 3:1 before in our solar system.  [1I/'Oumuamua appears unusually elongated in shape, with an axial ratio exceeding 5:1. – https://arxiv.org/abs/1711.11530 ] To understand how astronomers can hypothesis this, imagine a hot dog rotating in space.  When the hot dog’s long side is toward you, you see more of the surface.  That means more light is being reflected toward you.  When the end of the hot dog is toward you, you see less of the surface and therefore less light. One paper reports that the asteroid appears to be tumbling [https://arxiv.org/abs/1711.11530], this adds to the uncertainty of the shape of the object. It is roughly a quarter of a mile (half a kilometer) long. Currently, astronomers are stumped as to how such an object could form without breaking. According to one paper,  “Except for its unusually elongated shape, 1I/2017 U1 is a physically unremarkable, sub-kilometer, slightly red, rotating object from another planetary system.” [https://arxiv.org/abs/1711.05687]  It is most similar in albedo, a measure of reflected light, to what are called P and D type asteroids but night as red as the ultrared objects in the Kuiper belt. P-type asteroids are some of the darkest asteroids in the solar system.  They are slightly red in color and can be found in the outer asteroid belt.  There are 33 known P-type asteroids. D-type asteroids are also very dark and slightly red.  These can be found in the outer asteroid belt and most Trojan asteroids are of this type.  Trojan asteroids are those that share the orbit of Jupiter in what are called the “Lagrange points” on either side of the gas giant.  There are 46 known D-type asteroids. According to the NASA FAQ page, as of Nov. 20th, “the object [was] about 183 million miles (295 million kilometers) from the Sun, traveling outbound above the region between the orbits of Mars and Jupiter at about 89,000 miles per hour, or 40 kilometers per second. It [was] about 124 million miles (200 million kilometers) from Earth [on Nov. 20th].”  – NASA faq From orbital models, it is following a hyperbolic orbit and was closest to the sun on Sept. 9th, 2017 and would have been traveling 196,000 mph (87.4 km/s).  Interstellar speed estimated at 59,000 mph or 23.6 km/s covering the distance of a light year in about 11,000 years. Is it really from another solar system? Here is the Q & A from the NASA FAQ: “Are you really sure this object came from outside our solar system? Yes. The trajectory of this object has been tracked carefully since it was discovered, and its motion follows a hyperbolic path around the Sun. Basically, the high speed at which 1I/2017 U1 is traveling through the solar system cannot be due to acceleration from the Sun’s gravity alone. This object must have approached our solar system already with considerable initial speed. It is simply traveling too fast to have originated in our solar system. The object’s high speed also means that the Sun’s gravity cannot slow it down enough to keep it bound to our solar system. The object will leave, and end up with about the same speed with which it entered; only its direction will have changed.”  – https://www.nasa.gov/planetarydefense/faq/interstellar Orbital mechanics, the branch of physics dealing with motion in orbits, is a well understood field so the fact that the asteroid is heading out of the solar system unlikely to ever return is highly probable.  However, small gravitational perturbations make bigger and bigger differences as time progressing.  This is problematic when trying to make predictions (future or past) over long periods of time.  This is why no one is claiming which solar system the asteroid originally came from.  There is a possibility that `Oumuamua (pronounced ‘oh-oo-moo-ah-moo-a’) actually hails from closer to home.  The paper from Trilling et.al. summarized some other possibilities this way: “1I’s trajectory makes it very unlikely that it experienced a gravitational encounter with any of the proposed as-yet unknown planets in the outermost part of our Solar System (Trujillo & Sheppard 2014; Brown & Batygin 2016; Volk & Malhotra 2017).  Another possibility is that 1I was a member of our Solar System’s Oort Cloud and was perturbed inbound onto an unbound orbit by a passing star. We do not comment on these scenarios; in this work we have assumed that 1I is an interstellar interloper that originated in a different planetary system.” – https://arxiv.org/pdf/1711.01344.pdf So even though they did not investigate the likelihood of these scenarios, they did admit the possibility.  The asteroid is in an orbit that is not in the plane of the solar system.  That is to say, most planets orbit in, or close to the same disk in the same direction.  You can image the solar system as a plate with all the planets traveling along the surface of the plate.  This is another likely indicator that the asteroid comes from somewhere else but still does not rule out a local origin completely. The composition of the asteroid is consistent with other objects in our solar system.  The claims that it is red due to interstellar radiation are only speculation since we see similar features in solar system objects.  Reddening can be associated with interstellar travel but not necessarily evidence of it. In fact, the only really exceptional thing about this asteroid is its shape, and no one really has any theories, local or interstellar, on how this could happen. What we really need is more data.  Astronomers are going to track `Oumuamua (pronounced ‘oh-oo-moo-ah-moo-a’) as long as they can see it.  There are also preliminary talks about Space X’s Mars mission rocket sending a probe (with some gravitational assists from Jupiter) could catch up with the asteroid by 2039 (https://www.space.com/38919-interstellar-asteroid-mission-spacex-mars-rocket.html).  Astronomers also estimate that an interstellar asteroid or comet that we could currently detect should pass through our solar system once every 5 years.  Future survey telescopes could increase this into about 1 a year. So is this really an interstellar object?  I would give it a definite maybe. Maybe It’s Aliens Image courtesy of xkcd (https://xkcd.com/1919/). Many have suggested the odd shape of this asteroid is due to the fact that it is artificial, aka. its from an alien civilization.  Could it be that we have found the first evidence of a civilization other than the human race?  The short answer is maybe but probably not.  I am not going to get into a theological and philosophical discussion here, I will leave that for a future episode.  Odd things in nature are just that, odd.  Artificial objects against a background of natural objects are strikingly different.  Corey Powell, on his blog, Out There points this out very pointedly through a past example: “In 2002, astronomers noticed a small, fast-spinning object in an unusual Earthlike orbit. Spectroscopic observations revealed rough matches with aluminum and paint containing titanium oxide. The object was quickly identified as an Saturn V rocket upper stage, probably from Apollo 12” (http://blogs.discovermagazine.com/outthere/2017/11/23/interstellar-asteroid-mystery/).  There have been several odd occurrences in the recent past.   A weird signal back in July of this year in the direction of the star Ross 128 turned out to be reflections of geosynchronous satellites (https://www.cnet.com/news/ross-128-we
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