The Solar System is very tidy. You have four rocky planets near the Sun, and four gas giant planets further away. An asteroid belt with a dwarf planet separates the two groups, and many other small worlds exist beyond the orbit of Neptune. There is one kind of planet that doesn’t exist here, however: super-Earths, and a new discovery suggests that this type is a lot more common elsewhere than previously thought.
Super-Earths are worlds that are bigger than our planet but smaller than Neptune. There have been many discovered among the almost 6,000 confirmed planets, but the latest one sent researchers on a wider hunt, indicating that these planets are common and that our Solar System is not the standard of star systems in the galaxy.
The discovery comes from the detection of a microlensing event, OGLE-2016-BLG-0007. Gravitational microlensing is a phenomenon that occurs when a small body with mass, such as a planet, passes in front of a star, and the eclipse that is formed actually produces a little increase in light as the gravity of the planet magnifies the star behind.
OGLE-2016-BLG-0007 turned out to be special. It is about one-third heavier than our planet, and it orbits about 1.5 billion kilometers (over 930 million miles) from its star, which is 60 percent the mass of the Sun. That’s further away than Saturn is from the Sun.
“We found a ‘super Earth’ — meaning it’s bigger than our home planet but smaller than Neptune — in a place where only planets thousands or hundreds of times more massive than Earth were found before,” lead author Weicheng Zang, from the Center for Astrophysics (CfA), said in a statement.
The finding had researchers thinking: what are the chances of finding super-Earths at such large distances from their host star? To answer it, the team used the Korea Microlensing Telescope Network (KMTNet). Data from other microlensing events suggest that there is a super-Earth on a Jupiter-like orbit for every 0.35 stars. With an estimated 100 billion stars in our galaxies, there could be 35 billion super-Earths in the outer reaches of many star systems.
“This measurement of the planet population from planets somewhat larger than Earth all the way to the size of Jupiter and beyond shows us that planets, and especially super-Earths, in orbits outside the Earth’s orbit are abundant in the Galaxy,” said co-author Jennifer Yee of the Smithsonian Astrophysical Observatory, which is part of the CfA.
“This result suggests that in Jupiter-like orbits, most planetary systems may not mirror our Solar System,” said co-author Youn Kil Jung of the Korea Astronomy and Space Science Institute, which operates the KMTNet.
KMTNet uses three telescopes in Chile, South Africa, and Australia, and it is still growing. With more data, researchers will be able to refine not just the estimate but also the properties of these distant worlds. The planet from this event goes around its star every 40 years, so we won’t be seeing it again anytime soon.
“The current data provided a hint of how cold planets form,” said Professor Shude Mao of Tsinghua University and Westlake University, China. “In the next few years, the sample will be a factor of four larger, and thus we can constrain how these planets form and evolve even more stringently with KMTNet data.”
The study is published in the journal Science.
Source Link: “Super-Earths” Don’t Exist In The Solar System – But They’re Very Common Elsewhere