There's a solar system close to here that hosts an unusually active debris field, one in which a comet is annihilated every five minutes. Astronomers say it could be the result of gravitationally trapped debris — or the catastrophic collision between two planets the size of Mars.
The solar system, called Beta Pictoris, is located about 63 light-years from Earth. It formed about 20 million years ago, so it's a relative newcomer to the galaxy. It's got one known planet, Beta Pictoris b, located 1.2 billion kilometers from it and a mass several times greater than Jupiter's.
But it also features a prominent and luminous debris field — and within it, a unique compact cloud of poisonous gas orbiting at the solar system's outer fringes. It formed (and continues to be maintained) by rapid-fire collisions among a swarm of icy, comet-like bodies. Scientists have two theories to explain its presence: Either the frozen debris is trapped and held together by the gravity of a yet-to-be-discovered planet, or it's the remnant of a collision between two icy planets.
By using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, a team of international astronomers mapped the millimeter-wavelength light emanating from the dust and carbon monoxide (CO) molecules within the disk, revealing a rather disproportionate amount of the latter — about 0.3% of the mass of our moon. This gas is one of many found stored in comets and other icy bodies that, along with dust and icy grains, gets released after collisions.
Credit: ALMA (ESO/NAOJ/NRAO)/W. Dent et al.
Within this vast belt of carbon monoxide is a highly concentrated clump of gas located about 8 billion miles (13 billion km) from the star, which is about three times the distance between Neptune and our sun (85 AU). Remarkably, the total amount of CO measured exceeds 200 million billion tons, which is equivalent to about one-sixth the mass of Earth's oceans.
Now, it only takes about 100 years for ultraviolet starlight to break-up CO molecules, a duration much faster than the time it would take the cloud to complete a single orbit around the star. It's certainly possible that we're observing Beta Pictoris during this exceptionally small window of time. It's more probable, however, that something else is going on.
That something else, say the astronomers, is the continuous replenishment of carbon monoxide in the cloud, likely caused by the steady and frequent collisions between the icy celestial bodies within it. In fact, calculations show that to offset the dissipation of CO molecules, a large comet must be destroyed every five minutes.
The astronomers are now trying to figure out why. One possibility is that the solar system has an undiscovered giant planet, called a "shepherding planet," near the inner edge of the CO belt.
Credit: ALMA (ESO/NAOJ/NRAO) and NASA's Goddard Space Flight Center/F. Reddy.
Comparatively, Jupiter's gravity has trapped thousands of asteroids in two groups — a lead group and one following the gas giant along its orbit. Luckily, astronomers are able to observe Beta Pictoris nearly edge-on, allowing them to determine whether the CO belt has a single concentration of gas or two on opposite sides of the star. They're not entirely sure, but they're currently leaning towards the two-clump scenario. If that's the case, than further observations should reveal the second clump and the mystery planet.
But, if the astronomer's can't find the second clump, that leaves an alternative scenario: a crash between two Mars-sized icy planets around half-a-million years ago. This would account for the swarm, along with the frequent ongoing collisions among the fragments.
The results of the study now appear in Science.
[Via NASA | ESO]