One-third of planets orbiting our galaxy’s red dwarf stars could be in the ‘habitable zone’ — and could host extraterrestrial life, study claims
- Researchers used data from NASA’s Kepler telescope to study red dwarf stars
- Red dwarfs are very low in mass and make up the majority of the stars in our galaxy
Finding life on other planets has long been one of astronomers’ greatest quests.
Now a new study suggests the Milky Way galaxy has hundreds of millions of promising targets to search for signs of life beyond our solar system.
Using NASA’s Kepler telescope, researchers studied a small sample of planets orbiting red dwarfs — low-mass stars common in our galaxy.
They found that one-third of the planets — amounting to hundreds of millions in the Milky Way in total — likely have the right conditions to host life.
Scientists estimate that a third of the planets orbiting red dwarf stars in our galaxy “could harbor life.” Pictured is a planet orbiting a red dwarf – the most common type of star in our Milky Way galaxy
The new study was conducted by experts at the University of Florida and published in the journal The Proceedings of the National Academy of Sciences.
What are Red Dwarfs?
Red dwarf stars, also called M dwarfs, are the smallest, most abundant, and longest-lived stars in the galaxy.
Red dwarf stars are low-mass stars — they have masses about 0.08 to 0.6 times that of the Sun.
Due to their low brightness, individual red dwarfs cannot be easily observed.
“I think this result is very important for the next decade of exoplanet research, as the eyes shift to this population of stars,” said study co-author Sarah Sagear.
“These stars are excellent targets for looking for small planets orbiting where it is possible that water is liquid and therefore the planet is habitable.”
Our Milky Way galaxy is estimated to contain between 100 billion and 400 billion stars – and at least that number of planets.
Interestingly, only about 20 percent of the stars in the Milky Way galaxy resemble our sun, making it a “relative rarity,” according to the researchers.
By far the most common stars are red dwarfs, which are considerably smaller and cooler and have at most half the mass of our sun.
Red dwarfs make up most of the star population in the Milky Way — nearly 75 percent, according to estimates — and are about the size of Jupiter.
For their study, the researchers used new data from NASA’s Kepler telescope, which would capture information about exoplanets as they move in front of their host stars — known as “transiting.” This is an artist’s impression of the Kepler space telescope that was decommissioned by NASA in 2018 after nearly a decade of service
In addition, billions of planets orbit these ordinary dwarf stars in our galaxy, making them a particular target for astronomers.
Eccentric orbits and tidal heating
The more oval a planet’s orbit is, the more eccentric it is.
If a planet orbits close enough to its star, about the distance Mercury orbits the sun, an eccentric orbit can subject it to a process known as tidal heating.
As the planet is stretched and deformed by changing gravitational forces on its irregular orbit, friction heats it up.
At the extreme end, this could fry the planet, removing any chance of liquid water.
For their study, the Florida team measured the “eccentricity” of orbits of a sample of more than 150 planets around red dwarf stars in the Milky Way.
To measure the orbits of the planets, the researchers focused mainly on the time it took for the planets to move across the surface of the stars – also known as ‘transiting’.
Their study was also based on new data from the European Space Agency’s Gaia telescope, which has measured the distance to billions of stars in the galaxy.
“The distance is really the most important piece of information that we were missing before, which allows us to do this analysis now,” Sagear said.
To trap enough heat to be habitable, planets must huddle very close to their red dwarf stars, making them susceptible to extreme tidal forces, the astronomers say.
In their analysis based on the telescope data, the team found that two-thirds of the planets around the red dwarf stars could be toasted by these extreme tides, sterilizing them.
But that leaves a third of the planets — which amounts to hundreds of millions in the galaxy — that could be in a “goldilocks” orbit, close enough and soft enough to hold liquid water and possibly host life.
They also found that stars with multiple planets are most likely to have the kind of circular orbits that allow them to hold liquid water.
Meanwhile, stars with only one planet were most likely to see tidal extremes that would sterilize the surface.
The researchers say their findings “have implications for planetary formation and follow-up observations.”
New telescopes like the James Webb will now be the key to identifying water – an important sign of life – on ‘exoplanets’ (planets outside our solar system).
SORRY EARTHINGS: OUR SUN WILL BECOME A RED GIANT WITHIN ABOUT 5 BILLION YEARS BEFORE SHIMING INTO A COMPACT WHITE DWARF
The sun is only 4.6 billion years old during its life of about 10 billion years.
When the hydrogen fuel in the center of a star is exhausted, nuclear reactions will go out into the atmosphere and burn the hydrogen in a shell around the core.
As a result, the star’s exterior begins to expand and cool, making it much redder.
Over time, the star will turn into a red giant and grow to more than 400 times its original size.
As they expand, red giants engulf some of their nearby planets. In the case of the sun, this means the fiery end of all the inner planets of our solar system, which may include Earth.
But don’t worry – this won’t happen for another 5,000,000,000 years.
Once swollen into a red giant, engulfing the inner planets and scorching the Earth’s surface, it will shed its outer layers, leaving the sun’s exposed core as a slowly cooling white dwarf.
This stellar cinder will be incredibly dense, packing much of the sun’s mass into a sphere about the size of Earth.
Source: ESA/National Schools’ Observatory