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

By: April Carson

In a young star system called HD 172555, the ALMA ground-based radio telescope has discovered proof of a pair of terrestrial planets colliding about 200,000 years ago. Debris and dust were formed as a result of this collision, and one of the exoplanets may have lost its atmosphere, enriching the circumstellar environment with heavy metals.

When do planets clash, and what are the consequences?

Models of the formation of terrestrial planets indicate that in the final phases of the process, which can take tens of millions of years after the breakup of the protoplanetary disk, planets frequently collide with one another. It is thought that such catastrophes cause Earth-like planets to grow to their full sizes. One among the prominent versions of how the Earth got its mass is the "iron catastrophe" model which assumes that a considerable amount of iron from the core of an ancient Mars-sized planet was added to our world as the result of a collision with Earth.

Another consequence is that more stars will be born. At the same time, it's expected that there will be additional consequences of these collisions, such as debris formation. The system with an A-type star HD 172555 at a distance of 95 light-years from the Sun is considered to be the most convincing case of observations.

Atypical dust in HD 172555

The system is approximately 23 million years old, and earlier observations revealed significant quantities of warm dust with a unusually steep size distribution, in particular an overabundance of sub-micron-sized dust grains, and an atypical composition that includes tektite, obsidian, and silica monoxide. According to researchers, all of this can be explained by the collision of two roughly Earth-sized planets.

The outer shell of carbon monoxide molecules is seen 15 astronomical units from the star, where dust and gas are emitted. A ring with a radius of about 7.5 astronomical units and a width of about 3.3 astronomical units contains carbon monoxide (CO) emissions, which are observed within 15 astronomical units of the star. CO has a mass of 28 atomic mass units, and its transition is almost insensitive to the intensity of infrared radiation. It moves at a velocity of about , which corresponds to 20 kilometers per second. If this outer shell was created by one specific collision, it must have happened within the past 100–300 years.

Carbon monoxide

Under the influence of ultraviolet radiation, carbon monoxide in the circumstellar environment will photodissociation. As a result, the presence of this extremely flammable gas in the solar system's Main Asteroid Belt under normal conditions should be explained by recent mechanisms for generating or replacing CO reserves in the system.

The collision of bodies within the asteroid belt, the dispersion of CO from the system's outer regions, or a cataclysmic collision between objects roughly the size of a planet can all cause four such processes.

Collision of two planets in HD 172555

According to researchers, the most credible explanation for the HD 172555 system is a huge collision between two planets comparable in size to Earth and having a total mass of eight Earth masses that occurred at least 200,000 years ago.

A planet loses its atmosphere

At the same time, up to 60% of the CO 2 gas envelope surrounding a planet might be lost in a collision, which was subsequently transformed into CO by converting all of its hydrogen. The proportion of gas envelope removed may differ depending on the amount of CO and/or CO 2 present in lighter atmospheres dominated by molecular hydrogen or less massive planets with atmospheres dominated by atomic hydrogen.

The researchers, led by Dr Vanessa Bailey of the University of Arizona in Tucson, used Spitzer's Infrared Spectrograph (IRS) to detect both CO and CO 2 , two so-called "tracer" molecules that are commonly used to infer the amount of gas envelopes present around planets orbiting other stars. The team then used these data in computer models to simulate the chemical weathering of rocks on both planets, which use CO 2 and H 2 O as raw materials to produce minerals such as calcite (CaCO 3 ) and silicate rock types similar to those found on Earth.

They found that CO is about 30 times faster than CO 2 at weathering rocks in the hot, high-pressure conditions on the rocky planets. As a result, when two planets collide, the one with more CO will erode away faster than the other one.

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About the Blogger:

April Carson is the daughter of Billy Carson. She received her bachelor's degree in Social Sciences from Jacksonville University, where she was also on the Women's Basketball team. She now has a successful clothing company that specializes in organic baby clothes and other items. Take a look at their most popular fall fashions on

To read more of April's blogs, check out her website! She publishes new blogs on a daily basis, including the most helpful mommy advice and baby care tips! Follow on IG @bossbabymav





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