1I/‘Oumuamua, the first observed visitor from interstellar space, that swung by our Sun a month ago, has a rather unusual non-asteroid-like shape — that of an elongated cigar! At 400 meters long, it is ten times as long as it is wide. It is dark and has a somewhat reddish hue. And it spins every 7.3 hours as it travels through our galaxy, free from the bounds of any star.
No other solar system asteroid or comet sports such an extreme shape. The most elongated objects observed to date have an aspect ratio no greater than 3:1.
1I/‘Oumuamua (earlier known as A/2017 U1 and 1I/2017 U1) was discovered on Oct. 19 by the University of Hawaii's Pan-STARRS 1 telescope on Haleakala, Hawaii. The object approached our solar system from the direction of the constellation Lyra from "above" the ecliptic, the approximate plane in space where the planets and most asteroids orbit the Sun. On Sept. 2, the small body crossed under the ecliptic plane just inside of Mercury's orbit and then made its closest approach to the Sun on Sept. 9, traveling at a blistering 314,280 km per hour. The object made a hairpin turn around the sun, passing under Earth's orbit on Oct. 14 at a distance of about 24 million km - about 60 times the distance to the Moon. www.nasa.gov/…
As of Nov. 20, ‘Oumuamua is travelling at about 137,880 km per hour relative to the Sun. It is located ~200 million kilometers from Earth, lying between the orbits of Mars and Jupiter, its outbound path is about 20 degrees above the ecliptic. The object passed Mars’s orbit around Nov. 1 and will pass Jupiter’s orbit in May of 2018. It will travel beyond Saturn’s orbit in January 2019 and head towards the constellation Pegasus. Once it reaches interstellar space, it will be traveling at a leisurely 95,040 kmph. www.nasa.gov/...
Observations from large ground-based telescopes will continue until mid-December, after which ‘Oumuamua will become too dim to observe.
Here is a fascinating animation of the majestic asteroid as it scouted its way through the solar system -
How Did They Estimate its Size and Shape?
As described in eso.org/…, immediately after its discovery, researchers and telescopes around the world, including ESO’s Very Large Telescope in Chile and the Gemini Observatory in Hawaii, were called into action to measure the object’s orbit, brightness and color. A team of astronomers led by Karen Meech of the Institute for Astronomy in Hawaii found that ‘Oumuamua varies in brightness by a factor of ten as it spins every 7.3 hours. “This unusually big variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape,” said Meech.
Other Characteristics of ‘Oumuamua
‘Oumuamua is now believed to be a dense and rocky asteroid with a high metal content and no water or ice (hence no cometary tail). It’s dark and reddened surface is an indication of tholins, which are the result of organic molecules (like methane) being irradiated by cosmic rays for millions of years. The authors of the paper state that A/2017 U1 seems compositionally indistinguishable from similar objects in our own solar system despite its curious morphology.
The authors suggest that ‘Oumuamua may have been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with our Solar system. And it will probably never visit us again.
A/2017 U1 has likely orbited the galaxy multiple times and its system of origin could today be on the other side of the galaxy. This also suggests that the solar perihelion of A/2017 U1 was its first close encounter with a star and the first opportunity to warm any volatiles.
Here is a size comparison of ‘Oumuamua with other existing spacecraft, drawn approximately to scale -
Of course, we do not yet have any theories on how celestial objects can acquire and sustain such shapes.
So, how many ‘Oumuamua -like ISOs are out there?
Astronomers estimate that an interstellar object (ISO) similar to ‘Oumuamua passes through the inner Solar System (< 1 AU, AU = Earth-Sun distance) about once per year, but they are too faint to be easily detected. Comets with their long vapor tails are obviously much easier to spot. It is only recently that survey telescopes, such as Pan-STARRS, have become powerful enough to detect and study them.
Another independent paper, which uses data gathered using the NOT and WIYN Telescopes, confirms these findings about ‘Oumuamua and estimates that, at any one time, there are ∼10,000 interstellar bodies of U1-size closer to the Sun than Neptune (30 AU). Each takes ∼10 years to cross the planetary region before returning to interstellar space.
The Very Large Telescope
Here is a video on ESO’s Very Large Telescope (VLT) in Chile —
What’s in a Name?
1I/‘Oumuamua was earlier known as A/2017 U1 and 1I/2017 U1.
The "I" in the name, stands for interstellar object. A new designation "I" was established for interstellar objects by the International Astronomical Union, 1I/‘Oumuamua being the first object thus named.
The name ʻOumuamua was chosen by the Pan-STARRS team. The name is Hawaiian in origin (ʻou means reach out for, and mua, with the second mua placing emphasis, means first, in advance of), and reflects the nature of the object as a "scout" or "messenger" from the past. The first character is a Hawaiian ʻokina, not an apostrophe. en.wikipedia.org/…
What if Such an Object Collided with Earth?
The size and speed of ʻOumuamua implies that a direct collision with Earth would be catastrophic, perhaps not as much as the 10 km asteroid that hit Earth about 65 million years ago and wiped out the dinosaurs.
That is why NASA and other agencies around the world have been observing and cataloging asteroids for years now, using ground and space based telescopes and radar, and are experimenting with technologies to defend Earth against such an object should one happen to be on a direct collision course with Earth. Of course, interstellar asteroids are difficult to catalog and we just have to keep our planetary fingers crossed.
Planetary Defense Against Asteroids
A variety of techniques have been proposed for dealing with marauding asteroids. A few experimental missions have been conducted and others are in the pipeline. See earlier diary Asteroids and Planetary Defense for more info on these missions.
Unfortunately, NASA’s budget is getting squeezed, while its projects grow in number and complexity. One of the asteroid defense projects — the Asteroid Redirect Mission (ARM) — was canceled earlier this year. The House Appropriations Committee explained that decision by saying “The Committee believes that neither a robotic nor a crewed mission to an asteroid appreciably contribute to the overarching mission to Mars.”
Mars over civilization-destroying asteroids?
Remarks
So, we just caught a glimpse of ʻOumuamua on its quick visit to our Solar system. Was it really just an asteroid? What was it’s purpose? Have similar objects visited us before, unseen and undetected? Did it leave satisfied? It is time to let our imagination run wild ...
It does remind us of Rendezvous with Rama (the name Rama was actually suggested for ‘Oumuamua before the official name was decided upon — en.wikipedia.org/...) ...
… and the whale probe from the Star Trek IV movie -
References
- Solar System’s First Interstellar Visitor Dazzles Scientists — www.nasa.gov/…
- ESO Observations Show First Interstellar Asteroid is Like Nothing Seen Before — eso.org/…
- Research paper — DISCOVERY AND CHARACTERIZATION OF THE FIRST KNOWN INTERSTELLAR OBJECT — www.eso.org/…
- Paper in Nature journal — A brief visit from a red and extremely elongated interstellar asteroid — www.nature.com/…
- Interstellar Interloper 1I/2017 U1: Observations from the NOT and WIYN Telescopes — www2.ess.ucla.edu/… — another paper by a group from UCLA.
- First Known Interstellar Visitor is an “Oddball” — www.gemini.edu/…
- Earth's First Known Interstellar Visitor Unmasked — ifa.hawaii.edu/...
- Asteroids and Planetary Defense — www.dailykos.com/...