Astronomers Say Newfound Metal Planet as Dense as Mercury May Finally Reveal How Our Solar System Formed

Wednesday, 28 March 2018 - 10:21AM
Solar System
Science News
Wednesday, 28 March 2018 - 10:21AM
Astronomers Say Newfound Metal Planet as Dense as Mercury May Finally Reveal How Our Solar System Formed
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Image credit: NASA
Mercury is special among the planets in our solar system for a number of reasons (not least because Han Solo has been spotted frozen in carbonite on its surface!).

While Mercury is the closest planet to the sun, it's not actually the hottest lump of rock in the solar system—that honor goes to its immediate neighbor, Venus, which has a thick carbon dioxide atmosphere, showing the effects of greenhouse gasses.

Mercury is a heavy beast compared with the other planets in the solar system, and scientists have long speculated that its dense structure may suggest that it didn't form in the same way as the rest of the worlds in our familiar stretch of space.

Now, astronomers have managed to identify another planet that appears to be just as dense as Mercury, giving us an excellent opportunity to take a look at what might well be a subset of planets that we've not really considered before.

The planet, K2-229b, is approximately 20 percent larger than Earth, but conditions there are in no way similar to what we enjoy here at home. K2-229b, like Mercury, is very close to the star that it orbits, and it completes an orbit in just 14 hours—it was first spotted because scientists noted that the light from its star would periodically dip as K2-229b whizzed past.

The planet is made up of thick, dense metal, and temperatures on its day side reach over 2,000 degrees Celsius (3,600 Fahrenheit). It isn't exactly an ideal vacation spot, but considering that it's 339 million light-years away, this isn't too big of a loss. In the meantime, the planet gives us a good glimpse at what conditions might have inspired the creation of Mercury here in our own solar system.

According to Dr. David Armstrong of the University of Warwick:

Opening quote
"Mercury stands out from the other Solar System terrestrial planets, showing a very high fraction of iron and implying it formed in a different way. We were surprised to see an exoplanet with the same high density, showing that Mercury-like planets are perhaps not as rare as we thought.

"Interestingly K2-229b is also the innermost planet in a system of at least 3 planets, though all three orbit much closer to their star than Mercury. More discoveries like this will help us shed light on the formation of these unusual planets, as well as Mercury itself."

Closing quote

Considering that K2-229b is, like Mercury, the closest planet to its star, the position of these two bodies may have affected the way they developed. One theory suggests that, in both cases, the planets became so dense because strong solar winds whipped away their atmospheres shortly after their creation, causing a lot of their material to stay in a tight ball rather than expanding.

This ties in with a theory that suggests that the opposite happened to Jupiter, as gases leaked out to create a thick, dense atmosphere that gave birth to the gas giant world we know today.

Alternatively, another explanation for the creation of K2-229b is that the planet is the result of two giant objects in space that collided with each other—this instead ties into a theory surrounding the creation of the moon, after a rock the size of Mars crashed into the planet and chipped a large chunk from its surface.

Whatever the cause of K2-229b's unique form and density, there's going to be a lot more research in the coming months and years that will help us better understand these strange types of planets.

With any luck, we should get a better understanding of what happened during the formation of our own solar system in the process.
Solar System
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