They get cooked, and then shrink!
Stars, like our sun, are very beneficial to our planet — supplying warmth, light, and energy. However, sometimes stars can be pretty destructive, smothering planets with powerful radiation, and even stripping away their atmospheres.
Astrophysicists at the University of Birmingham have used data from the NASA Kepler space telescope to discover something many astronomers have long suspected: a class of exoplanets whose atmospheres have been peeled away by their host stars.
According to the study, published on April 11 in the journal Nature Communications, planets with gaseous atmospheres that lie very close to their host stars are bombarded by high-energy radiation. Unfortunately, due to their proximity to the star, this intense heat blows away their atmospheres. This violent “stripping” occurs in planets that are made of a rocky core with a gaseous outer layer.
One of the researchers, Guy Davies of the University of Birmingham’s School of Physics and Astronomy, said in a press release, “For these planets it is like standing next to a hairdryer turned up to its hottest setting.”
“Stars are big old balls of gas,” explained Davies in a Skype interview with The Christian Science Monitor (CSM). “The ones we study aren't massively dissimilar to the sun – perhaps up to 1.5 times its mass.”
However, these stars have massive amounts of acoustic energy that are trapped by the vast vacuum lying outside — known as space — and it is this sound energy that the research team analyzed.
This type of sound energy is the basis for asteroseismology — the natural resonances of stars. Asteroseismology gets more accurate the longer you keep analyzing the same area, so by using it along with complex statistical analysis, the team characterized the properties and inner structures of these stars and their planets with an accuracy not achieved before.
“There has been much theoretical speculation that such planets might be stripped of their atmospheres,” Davies continued in the release. “We now have the observational evidence to confirm this, which removes any lingering doubts over the theory.”
To confirm the theory, the scientists plotted the data on a chart and compared the amount of radiation various planets were receiving to the radius of those planets. However, as they were plotting the data, their attention was drawn to a very specific area on the chart: A section of planets in an area that should have been populated by hot “super-Earths” — planets a little larger than Earth, but so much hotter because of the proximity to their star.
The astrophysicists concluded that although the planets were still physically located where they were expected, they had indeed changed: their radius had altered. “The high radiation levels have burned off the atmosphere,” said Davies to CMS. “Radiation from the star has heated up the gaseous environment and it's burned away.”
All that remains is the planet’s rocky core.
The results of the study have important implications for understanding how star systems, just like our own solar system, evolved over time and the role played by the host star.
“Our results show that planets of a certain size that lie close to their stars are likely to have been much larger at the beginning of their lives. Those planets will have looked very different,” explained Davies in the media release.
“We haven't found a system where this is actually happening yet — we simply detect an absence of these planets, when they should be there,” said Davies to CSM. “What we need to do now is to find one of these planets undergoing this stripping, or just having done it, and look at the dynamic processes.”
Scientists hope that they will discover and characterize these “stripped systems” by using a new generation of satellites, including the NASA TESS Mission which will be launched next year.
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