Astronomers see hot fragments of colliding planets

A new measurement shows that the debris of this cosmic crash still pops regularly.


Impression of the colliding planets.
Impression of the colliding planets. Image: NASA


At a distance of three hundred light years from the earth, dust is swirling through a planetary system, indicating that two planets have recently collided there.

The astronomers discovered the dust in BD +20 307, a system of two stars orbiting around each other. Both stars are at least a billion years old.

Usually in such an old system things go quietly. Dust that in the early years of the system still swayed through the space between the star and the planets, has now disappeared. 

It has either fallen into the star or it has been blown by the star to the outer edges of the planetary system.


At BD +20 307 it is a different story. Astronomers discovered a lot of dust there, which is also warm. They suspect that the dust flew off when two planets recently exploded and broke into pieces.


Flying Observatory

The fact that BD +20 307 contains hot dust has been known for some time. Ten years ago, space telescope Spitzer was the first to detect the hot dust. 

The older measurement has now been confirmed by SOFIA (Stratospheric Observatory For Infrared Astronomy), a flying observatory that consists of a telescope mounted on a modified Boeing.

SOFIA also saw that the amount of heat radiation in BD +20 307 has increased by ten percent in recent years: a sign that there is now even more hot dust than before. This underscores the idea that planets have recently collapsed in the system.


Astronomers see hot fragments of colliding planets
Astronomers see hot fragments of colliding planets


Colliding planets

The great collision may have happened hundreds of thousands of years ago (which is still recent, by cosmic standards). What astronomers now see are collisions between the resulting debris, which spinning around and regularly collapsing on top of each other.

It is a rare opportunity to study catastrophic late collisions in a planetary system,' says research leader Alycia Weinberger of the American Carnegie Institution for Science. 

The SOFIA measurements show that the dust disk changes in just a few years' time. Weinberger and her colleagues study was published in The Astrophysical Journal.

The researchers argue that it is also possible that the hot dust may not originate from a collision at all. For example, the dust may have moved closer to one of the stars, where the starlight heats it up more than before. But given the speed of the changes, that is not the most obvious explanation. Such movements usually take much longer than ten years.

Moreover, catastrophic collisions in planetary systems are not uncommon. It is likely that in the past the earth has also been the victim of a cosmic blasts. 

Astronomers think that 4.5 billion years ago a celestial body of the size Mars collided with the earth. The debris that flew off the planet, later formed the moon.

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