The orbital region around a star in which an Earth-like planet can have liquid water on its surface and possibly support life. Because liquid water is necessary for all life on Earth, the definition of a habitable zone is based on the assumption that extraterrestrial life would have the same need. This is a very conservative (but observationally useful) definition because a planet’s surface temperature is affected by factors such as atmospheric greenhouse gases, reflectivity, and atmospheric or oceanic circulation, in addition to its proximity to its star.
Furthermore, internal energy sources such as radioactive decay and tidal heating have the potential to warm a planet’s surface to the melting point of water. These energy sources can also sustain subsurface reservoirs of liquid water, allowing a planet to harbor life even if it is outside of its star’s habitable zone. The search for a habitable world where alien life might thrive has hit a new snag. According to scientists, an extremely large number of stars continue to eat their own planets as small snacks.
According to research published Monday in Nature Astronomy, not only do 30 to 35 percent of Sun-like stars consume several of their own planets but there are signs that astronomers can look for to determine which stars indulged in a little planetary snack. Not only does this provide valuable insight into how other star systems grow and behave, but it may also assist astronomers searching for habitable worlds in determining which systems they can safely ignore, according to Science Magazine.
The search for a habitable world where alien life could be thriving has hit a new roadblock. An extremely large number of stars, scientists say, keep swallowing their own planets as little snacks.
Iron Overload
The Astronomical Observatory of Padua scientists behind the study discovered that certain chemical signatures in stars can serve as clear indications that they consumed their planets after studying 108 binary systems with Sun-like stars.
Scientists from the Astronomical Observatory of Padua examined 108 binary systems with Sunlike stars and discovered that certain chemical signatures can be used to determine whether or not their planets were consumed. According to Lorenzo Spina, a Padua researcher, if a star is unusually rich in iron but not other elements such as carbon or oxygen, it can be interpreted as evidence of planetary engulfment.
“If a star is anomalously rich in iron but not in other elements such as carbon and oxygen, this can be interpreted as a signature of planetary engulfment,” said Lorenzo Spina, a Padua researcher, and lead study author.
This isn’t the first time scientists have looked into planetary engulfment, but this new study used a much larger set of data than previous research, providing a much clearer picture of what’s going on.
“This is clearly a strong trend,” said NASA astronomer Eric Mamajek, who was not involved in the study. “This is likely to become one of the classic papers on this subject.” All of this means that scientists searching the cosmos for potentially habitable worlds can save time by first looking at the stars. If a good candidate star is composed primarily of lighter elements such as hydrogen, helium, oxygen, and carbon, it is likely that it did not snack on its planets.
Around 40 planets, including the nearest extrasolar planet, Proxima Centauri b, and three planets in the TRAPPIST-1 system, have been discovered that are roughly Earth-sized and orbit within their stars’ habitable zones. Astronomers have also used climate simulations of other extrasolar planets, such as Kepler-452b, to determine that they may have surface water under the right climatic conditions.
A habitable zone’s inner boundary is where water would be lost due to a runaway greenhouse effect, in which greenhouse gases in a planet’s atmosphere trap incoming infrared radiation, causing the planet to become hotter and hotter until the water boiled away. The outer boundary is the point at which such greenhouse warming would be unable to keep surface temperatures above freezing anywhere on the planet. Astronomers have calculated the size of the habitable zone for a variety of stars. For example, the Sun’s habitable zone is currently estimated to extend from about 0.9 to 1.5 astronomical units (the distance between Earth and the Sun).
