Exoplanet System Discovered in Habitable Zone Around Nearby Star
On February 23, 2017, NASA published an article with Nature, the scientific journal, about a recently discovered solar system, called Trappist-1.
Trappist-1 is a solar system about 40 light years away, or roughly 235 trillion miles, from Earth. In the system, there are seven planets orbiting around a red dwarf star.
Exoplanets are planets that orbit around a star that is not in our own solar system. In the Trappist-1 system, all of the exoplanets are “terrestrial planets,” which means that they are rocky and dense, in contrast with gaseous planets which are not found in the Trappist-1 system. Gaseous planets may have a small rocky core, but the majority of the planet is made of gasses such as hydrogen and helium. These gas-giant planets are found in many solar systems, including our own solar system: Jupiter, Saturn, Uranus, and Neptune.
A red dwarf star, which is at the center of the Trappist-1 system, is a small and relatively cool and dim star. This particular star has less than eight percent of the mass of our sun, which means that the rate of fusion is extremely low.
“What’s unusual about this system is these planets were found around a dwarf star, a red dwarf,” Professor Chris Impey said.
Impey is a Distinguished Professor of Astronomy and Associate Dean of Science at the University of Arizona. Prof. Impey also spearheads the Active Galactic Videos team.
“Up until now, there were a number of terrestrial planets that had been found,” Impey said. “The total count of exoplanets is almost 4,000 and there are a couple hundred of earth-like planets, but almost all of those have been found around Sun-like stars.”
Since a dwarf star gives off little visible light and is brightest in infrared light, telescopes like the Spitzer infrared space telescope use this light to observe the dimming of the star as the planets pass in front of it each time they orbit.
Along with the small size of Trappist-1 dwarf star and the planet’s terrestrial landscapes, the planets orbit their star very quickly.
“All of these seven planets orbit [their star] in two weeks or less, and the fastest of the seven planets orbits in little more than a day or two days,” Impey said.
The planets’ orbits are actually how they were found. While many planets are discovered using the Doppler Method, which measures the movement of a star’s spectrum from its central location, the Trappist-1 planets were discovered using the transit method.
“With the period of the orbit of the planet, the planet crosses the star and dims it slightly,” Impey said. “Each planet dims the star sequentially.”
The process of a planet crossing, blocking, and dimming the light emitted from a star allows astronomers to deduce how many planets there are in the system and what their orbit is around their star.
Discovering the planets was a collaborative effort of international space agencies. The initial discovery was made using the Transiting Planets and Planetismal Small Telescope (TRAPPIST), a Belgian robotic telescope in Chile, hence the name of the solar system. Other telescopes, such as the Spitzer Space Telescope run by NASA, supplemented data for this discovery.
“It’s a highly international field,” Impey said.
But the importance of cooperation between space agencies and the large size of the solar system aren’t the only things that make this discovery remarkable; there is a possibility of liquid water to be on three of the seven planets.
“It has three of these planets in what is called the habitable zone, which are distances from the sun where water can be liquid,” Impey said. “In our solar system, pretty much only Earth is a habitable planet.”
In order to find evidence of life on the three planets, astronomers search for biomarkers, which are pieces of evidence for life found in the atmosphere; on Earth, a biomarker is oxygen in the atmosphere. If there is evidence of biomarkers in other planets’ atmospheres, then there is a possibility of the planet currently or previously sustaining life.
“There are ground-based and space-based facilities that could do this experiment to detect life on these exoplanets in the next decade,” Impey said.
In the future, the James Webb Space Telescope will be used to search for exoplanets. It will be the largest telescope launched into space and one of its’ main mission is to search for biomarkers and thick atmospheres on distant planets. The Webb Space Telescope is spearheaded by the European Space Agency and NASA and is set to launch in October 2018.
To read the full Nature report, visit their website.