'First' interstellar asteroid 'Oumuamua is dark red and elongated

Finally, more is known about the first interstellar asteroid ever found in our solar system. The object was discovered last month with the Pan-STARRS 1 telescope in Hawaii.

The asteroid was some 30 million kilometers from the earth in mid-October. The speed at that time was 26 kilometers per second. The orbit of the object in particular stood out. Astronomers look at the eccentricity of the orbit. That is the extent to which a lane deviates from a circle. The orbit of C / 2017 U1 PANSTARRS turned out to have an eccentricity of 1.2, making it a hyperbole. This means that it is impossible that the object revolves around the sun and therefore comes from outside the solar system.

Several telescopes zoomed in on the strange celestial body shortly after the discovery, including ESO's Very Large Telescope. These observations show that the object is dark, reddish and elongated. In addition, the interstellar asteroid consists mainly of rocks or metals. The research paper appears in the scientific journal Nature and can be read online here. An artistic impression of the asteroid can be seen at the top of this article.


A combined photo of different telescopes with our interstellar visitor in the center: 'Oumuamua. Credit: ESO / K. Meech et al.

The asteroid is called 'Oumuamua. 'Oumuamua turns around its axis every 7.3 hours and the object becomes up to ten times clearer. This means that the interstellar visitor has an unusual form. "It is about ten times as long as it is wide," says scientist Karen Meech. "We have also discovered that the object has a dark red color, similar to the objects in the outer area of ​​our solar system." The surface of 'Oumuamua has probably become red due to cosmic rays.

Here you can see the light curve of 'Oumuamua well. The asteroid reached an apparent magnitude of 22 last month. In comparison: Hydra - a small moon of Pluto - has a maximum brightness of +22.9.

The research also shows that 'Oumuamua is at least 400 meters long. Orbit calculations show that the asteroid came from the direction of the star Vega and is currently shooting through the Milky Way as an unguided projectile. The object probably roamed through our galaxy for hundreds of millions of years before it stumbled upon our solar system by accident.

Scientists think that the inner part of our solar system receives one interstellar guest every year. Often these objects are so weak that they cross the border area unnoticed. Thanks to a telescope like Pan-STARRS, it is finally possible to look for these visitors in a much more targeted way. "Now that we know that we have discovered the first interstellar rock, we are preparing for the next," concludes scientist Olivier Hainaut of ESO.