Two Planets Collide in Outer Space, One of Them Loses its Atmosphere

With a greater focus on
asteroids and objects from deep space, as well as the possibility of a
collision with Earth, astronomers have arrived for the first time at a planet
that may have lost its atmosphere as a result of a collision with a massive


A team of astronomers has
discovered an Earth-like planet that may have lost some of its atmosphere owing
to a collision 200,000 years ago. Astronomers from MIT, the National University
of Ireland Galway, and Cambridge University uncovered evidence of the massive
collision in a neighboring star system, only 95 light-years away from Earth.
The star, known as HD 172555, is roughly 23 million years old, and astronomers
believe its dust shows indications of a recent collision.


According to the study published
in the journal Nature, massive impacts are what cause planets like the early
Earth to reach their ultimate mass and attain long-term stable orbital
arrangements. One significant prediction is that these impacts will generate
debris. The astronomers reported “detection of a carbon monoxide gas ring
co-orbiting with dusty debris around HD172555 between about six and nine
astronomical units — a region analogous to the outer terrestrial planet region
of our Solar System.”

Astronomers have been intrigued
by star HD 172555 owing to the peculiar composition of its dust, which
presumably includes substantial amounts of strange minerals in grains that are
considerably finer than astronomers would anticipate. The study's lead author,
Tajana Schneiderman, a graduate student in MIT's Department of Earth,
Atmospheric, and Planetary Sciences, combed through data from Chile's Atacama
Large Millimeter Array (ALMA) for traces of carbon monoxide surrounding nearby


The ALMA observatory is a
network of 66 radio telescopes whose spacing can be changed to improve or
reduce picture resolution.

“When people want to study gas
in debris discs, carbon monoxide is typically the brightest, and thus the
easiest to find. So, we looked at the carbon monoxide data for HD 172555 again
because it was an interesting system,” Schneiderman said. After a thorough
review of the data, the researchers discovered carbon monoxide, which accounted
for 20% of the carbon monoxide detected in Venus' atmosphere.

The gas was circulating in vast
quantities, shockingly near to the star, at around 10 astronomical units, or 10
times the distance between Earth and the sun. The presence of such a massive
volume of gas surrounding the star demanded an explanation, and the researchers
worked on many possibilities.

Astronomers considered
scenarios in which the gas was created by the debris of a freshly born star, as
well as one in which the gas was produced by a close-in belt of ice asteroids,
but both were rejected. The best fit scenario considered by the study is that
the gas was leftover of a massive impact.

“Of all the scenarios, it’s the
only one that can explain all the features of the data. In systems of this age,
we expect there to be giant impacts, and we expect giant impacts to be really quite
common. The timescales work out, the age works out, and the morphological and
compositional constraints work out. The only plausible process that could
produce carbon monoxide in this system in this context is a giant impact,"
Schneiderman said in a statement.

The team believes the gas was
expelled by a massive collision at least 200,000 years ago, which was recent
enough that the star did not have time to totally destroy the gas. Based on the
quantity of the gas, the collision was most likely huge, involving two
proto-planets around the size of the Earth.

Astronomers believe that the
collision was so powerful that it blasted off a portion of one planet's
atmosphere, resulting in the gas observable today.


Research paper |