Finding worlds where liquid water could exist beyond Earth is one of the great undertakings in space science. Astronomy fans start buzzing whenever a planet is discovered in the habitable zone around a star. And we know this habitable zone isn’t constant.
Our solar system’s habitable zone includes Earth and Mars. One teaming with life. The other, a desolate wasteland. The TRAPPIST-1 system shows us the habitable zone can be incredibly close to the star. Thanks to a much cooler star, several planets sit within a habitable zone closer than Mercury’s orbit to its star.
The type of star matters. The habitable zone around our Sun is much different than the zone around TRAPPIST-1. Plus, there are even more exceptions. Take Europa and Enceladus. Both tiny moons are believed to have liquid water thanks to warming from the gravitational tug of war between them and the planets they orbit (Jupiter and Saturn, respectively).
Researchers from Cornell University are throwing in another way for planets to be habitable. Volcanoes.
Lead author Ramses Ramirez, a research associate at Cornell’s Carl Sagan Institute touches on the new research. “On frozen planets, any potential life would be buried under layers of ice, which would make it really hard to spot with telescopes.” Ramirez adds, “but if the surface is warm enough – thanks to volcanic hydrogen and atmospheric warming – you could have life on the surface, generating a slew of detectable signatures.”
Adding volcanoes and the hydrogen they produce to the equation expands a star’s habitable zone in a big way. Planets that would be balls of ice turn into warm worlds capable of holding water. If there are volcanoes. “You get a nice big warming effect from volcanic hydrogen, which is sustainable as long as the volcanoes are intense enough,” says Ramirez.
The hydrogen “puffs up” a planet’s atmosphere, making the detection of other chemical signatures easier with the next-generation of telescopes.
A star’s habitable zone expands 30-60% to account for this new research. Instead of the zone extending just beyond Mars, it could reach the asteroid belt between Mars and Jupiter. If Ceres was an Earth-like planet with just enough volcanic activity, it could potentially support life.
This bump in a star’s potential habitable zone means “adding a lot more planets to our ‘search here’ target list,” according to Ramirez.
Take the recent news about TRAPPIST-1. Add the potential for volcanoes and volcanic hydrogen to the mix and instead of three planets within the star’s habitable zone, you could have four. “Although uncertainties with the orbit of the outermost TRAPPIST-1 planet ‘h’ means that we’ll have to wait and see on that one,” says Lisa Kaltenegger, Cornell professor astronomy and director of the Carl Sagan Institute.
While a star has a lot to do with where a habitable zone lies in a solar system, there are a lot of other variables at play too. Tidal flexing on moons near much larger planets. And now, volcanoes.
This new research expands where astronomers can look. Now, the technology needs to catch up. That’ll start in 2018 with the launch of the James Webb Space Telescope and 2024 with the first observation from the European Extremely Large Telescope. These two telescopes can likely detect atmospheric biosignatures such as methane in combination with ozone, a signal for life.