collision of two planets

Planet SMASH! A celestial body about the size of our moon collides with a planet roughly the size of Mercury in a new artist's conception. Scientists think a scene like this played out just a few thousand years ago around a young star called HD 172555.

NASA's Spitzer Space Telescope recently detected the signatures of vaporized and melted rock along with rubble around the star, about a hundred light-years from Earth. Debris from a similar giant impact between Earth and a Mars-size body is thought to have created our moon about 30 to 100 million years after the sun formed.

And here's the ArXiv paper from way back in June.
http://arxiv.org/abs/0906.2536

All hail the Beta Pictoris moving group!

Sorry.

Has this star also a disc of dusts as that of Beta pictoris? Where dusts around her do come only from collision?

Stalker wrote:

Has this star also a disc of dusts as that of Beta pictoris?

It certainly does now.

Stalker wrote:

Where dusts around her do come only from collision?

Collisions are usually the cause of dust, yes. At HD 69830, the presence of dust is maintained by collisions between asteroids. It seems that at HD 172555, the dust was caused by the collision of two planets.

The Beta Pictoris moving group is made of stars that typically have protoplanetary disks that are in the process of forming planets.
Examples (all of which have disks):
AU Microscopii
Beta Pictoris
V343 Normae
HD 15115
HD 172555
HD 181237

From the arXiv paper linked by Sirius_Alpha upthread...

Quote :

In an HST/ACS coronagraphic mode search for scattered light from circumstellar dust around members of the β Pic moving group (Ardilla et al. 2009, in preparation), [b]no extended emission was detected around HD172555 to the limits of the size of the coronagraphic disk (0.5" radius or 15 AU at 29 pc) – so any significant circumstellar material must be localized inside 15 AU.

Curiously we could have missed something interesting back in August

A model for the optical flares from the Galactic tran-sient SWIFT J195509+261406

Quote :

The Galactic hard X-ray transient SWIFT J195509+261406 was first observed as a gamma-ray burst GRB 070610. Within 3 days after the burst, more than forty optical flares had been observed. Here we propose that this peculiar event should be associated with a white dwarf. The hard X-ray burst itself may be triggered by the collision between two planets orbiting the white dwarf. Some cracked frag-ments produced in the collision then fall onto the surface of the white dwarf in several days, giving birth to the observed optical flares via cyclotron radiation. Our model can satisfactorily explain the basic features of the observations.

Emphasis mine.

Hmm. I don't know how others search habits are, but when I comb arxiv, I just look at the abstracts and open whatever looks interesting in a new tab. I can see how it would've been missed.

Interesting though.

Plus the authors assume the planets are nearly equal mass (M=10²⁷ g i.e roughly 0.17 Earth masses, two Mars-sized objects then) and located 10¹² cm (i.e 0.0666 AUs) away from the star (or pulsar, it's not clear...).

Back to HD 172555...

A Self-Consistent Model of the Circumstellar Debris Created by a Giant Hypervelocity Impact in the HD172555 System
http://arxiv.org/abs/1210.6258

Refining the models...