The holy grail in the world of exoplanets seems to be finding a habitable, Earth-like planet. And it’s appealing. Thinking really long term, we can’t stay on Earth forever and having a backup planet might be the way to save humanity. But while we can’t say for sure that Earth-like planets are rare, they are hard to find; they’re small and have to orbit their star in that magic “goldilocks” zone where water can exist as liquid on the surface. Hard to find, but not impossible. The latest exoplanet discovery looks to be a super-Earth orbiting a nearby star in the goldilocks zone. It just might be the exoEarth astronomers have been looking for. Maybe. It’s still technically a candidate planet – we’re still waiting on astronomers to confirm the data.
Calling a planet a super-Earth is a little misleading. It’s not like the Earth on steroids with better water, nicer plants, and prettier people. It’s a planet that has up to ten times the mass of the Earth without being a gas giant.
The planet in question, called HD 40307g, is the furthest of six bodies orbiting the star HD 40307, which is a little over 40 light years from the Earth. The star in question is called HD 40307. It’s a dwarf star, cooler, dimmer, and smaller than the Sun but not by much making it pretty close to Sun-like. It also appears to be about the same age as the Sun, roughly 4.5 billion years old.
The planet was found with a time-tested method of looking at the mutual gravity a star and planet exert on one another. Using HARPS, the High Accuracy Radial Velocity Planet Searcher that looks for changes in light from a star as a planet orbits around it, astronomers can see starlight Doppler shifted as the planet tugs on the star during its orbit. By measuring the star’s Doppler shift, astronomers can determine the mass of the orbiting planet.
Though the data on the system was gathered a while ago, astronomers only recently found HD 40307g. The preliminary data suggests it’s seven times as massive as the Earth and orbits its star every 198 days. And it looks to be orbiting about 55 million miles from its star. That’s closer than we are to the Sun – we’re about 93 million miles. But since HD 40307 is fainter the different balances out and the new exoplanet rests firmly in its star’s goldilocks zone.
What’s missing still is how big the planets is. It could be the same size as the Earth but dense, or it could be much bigger and less dense. But there’s a chance it could be just right, with a mass and density like the Earth it could have an equivalent gravitational pull.
That one missing piece aside, it’s an exciting find. And perhaps the implications more so. Finding a potentially Earth-like planet in an Earth-like system could mean that Earths aren’t as rare as we once thought. Maybe the universe is actually teeming with Earths in their star’s goldilocks zones. Which I suppose means it’s possible that the universe is teeming with alien races on these exoEarths, but I won’t put my money on that idea just yet.