Exoplanet Found Orbiting Trio of Stars

The Cosmic Companion
· 5 min read

A newly-discovered exoplanet with the catchy name of LTT 1445 A b lives in a solar system containing three suns. This rocky world orbits one of the stars, which in turn orbits two others. The system sits just 22 light years from Earth, placing this planet well within our cosmic neighborhood.

The surface of this world is as hot as an oven — roughly 160 degrees Celsius (320 Fahrenheit), and the planet orbits its nearest sun once every five days. This super Earth has a mass around 2.2 times the mass of our home planet contained in a world just 38 percent larger than our own. This high density of LTT 1445 A b suggests it is almost certainly rocky. The views from the surface of this scorching hot world, however, would be surreal for any observer who set foot on the planet.

An artist’s conception of the view from the surface of a world in a triple star system. Image credit: ESO/M. Kornmesser

“If you’re standing on the surface of that planet, there are three suns in the sky, but two of them are pretty far away and small-looking. They’re like two red, ominous eyes in the sky,” Jennifer Winters, astronomer at the Harvard-Smithsonian Center for Astrophysics states.

The planet was found through the transit method, in which astronomers note the dip in brightness seen from stars as planets orbit in “front” of their suns, as seen from Earth. Periodic dips in the amount of light received from the star can betray the presence of an unseen planet. By measuring the amount of light lost, astronomers determine the diameter of the world. When that body passes “behind” its sun, a much-smaller dip in brightness reveals the brightness of the exoplanet.

A second method, looking at the gravitational “tug” a planet makes on its local star, allows researchers to calculate the mass of that world.

At just 22 light years from our own solar system, LTT 1445 A b is our second-closest neighbor ever discovered via the transit method of planet detection. The only transiting star system closer to us — HD 219134 bc — is roughly 21 light-years away from Earth.


This artist’s conception imagines the TRAPPIST-1 system, as two planets transit as they pass between their sun and an observer on Earth.

That’s One More Sun than Tatooine!

Each of the three stars in the LTT 1445 system are red dwarfs. These small, cool stars do not burn as brightly as yellow stars like our Sun, but they live for far longer periods.

“This isn’t the first three-star system to be found with at least one planet. Our nearest stellar neighbor, in fact, is Proxima Centauri, orbiting the more distant pair, Alpha Centauri A and B. Proxima is only 4.25 light-years away from Earth. In orbit around it is Proxima b, a small, probably rocky world that takes an estimated 11 days to circle its star,” NASA reports.

Most stars in our galaxy exist in systems with two or more stars.

The star LTT 1445 A holds on to roughly one-quarter of the mass of our Sun, at a surface temperature of just 3,100 degrees Celsius (5,600 Fahrenheit). Our local , by comparison, radiates at 5,500 degrees Celsius (9,900 Fahrenheit).

Orbiting just 5.7 million kilometers (3.5 million miles) from LTT 1445A, this world is far too close to its parent star for water to exist on its surface, making chances of life on that world highly unlikely.

The two companion stars in the system orbit their neighbor once every 36.2 years.

The TESS spacecraft, seen here in an artist’s conception, will search more than 200,000 stars, looking for planets orbiting alien stars. Image credit:NASA’s Goddard Space Flight Center/CI Lab

The planet was discovered by the Transiting Exoplanet Survey Satellite (TESS), searching the skies for signs of undiscovered worlds orbiting alien stars. This orbiting observatory was designed to search for transiting exoplanets, as they pass in front of their parent stars. This mission, launched in 2018, is expected to discover thousands of planets over its operational lifetime.


The Atmosphere is Out of Sight!

The mass and size measured for LTT 1445 A b suggests it is a rocky world, much like the planets of our inner solar system. It may still possess some atmosphere, an idea which intrigues researchers.

As astronomers watch exoplanets pass in front of their suns, light shining through the planetary atmosphere can reveal the chemical makeup of the air surrounding the alien world. When light is passed through a spectroscope, it is broken up into a rainbow of colors, like a rainbow. Dark lines in the spectra, known as absorption lines, reveal the chemical composition of any gases, including atmospheres, through which the light passes.

Light from stars or galaxies passing through gas develop distinctive patterns of dark absorption lines, like the ones seen in this spectrum. Each element has a telltale “fingerprint,” allowing astronomers to determine the chemical makeup of atmospheres on distant worlds. Public domain image.

If this exoplanet possesses an atmosphere, the short orbital period of the world will allow astronomers frequent opportunities to analyze the air. The dim star is also bright enough to produce useful readings without drowning out the planet in light.

“The planet provides one of the best opportunities to date for the spectroscopic study of the atmosphere of a terrestrial world,” researchers wrote in The Astronomical Journal.

“I’ve been studying the planets and learning the personalities of each planet.” — Dr. Dre

A size comparison of LTT 1445 A b and the Earth, created in the NASA Exoplanet Catalog.

In 2016, an exoplanet designated HD 131399Ab was discovered in a three-star system. However, the exoplanet in that system is a giant compared to the relatively small world found in the LTT 1445A system.

Technology for studying the atmospheres of exoplanets is still being developed, but this branch of astronomy is off to an exciting start. By studying LTT 1445 A b, astronomers hope to learn more about the nature of rocky planets orbiting red dwarf stars.

The James Webb Space Telescope (JWST), due for launch in 2021, could find thousands of exoplanets, as it explores the surfaces and atmospheres of distant worlds. Astronomers are currently compiling a list of exoplanets they would like to examine with Hubble, and LTT 1445 A b is on that list, waiting further exploration.


Did you like this article? Subscribe to The Cosmic Companion Newsletter!

The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

The Cosmic Companion

Written by

James Maynard is the author of two books, and thousands of articles about space and science. E-mail: thecosmiccompanion@gmail.com

The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

Welcome to a place where words matter. On Medium, smart voices and original ideas take center stage - with no ads in sight. Watch
Follow all the topics you care about, and we’ll deliver the best stories for you to your homepage and inbox. Explore
Get unlimited access to the best stories on Medium — and support writers while you’re at it. Just $5/month. Upgrade