NASA’s Hubble Telescope Observed Earth-Sized Planet Orbiting a Red Dwarf Star Just 22 Light-Years Away

Twenty-two light years away from Earth, a rocky world orbits a red dwarf. Scientists confirmed this to be the closest Earth-sized world to our Solar System.

Nearest Transiting Earth-Sized Planet

The transiting object is named LTT 1445 Ac, an exoplanet which measures 1.37 times the mass and 1.07 times the radius of the Earth. It lives in an unusual system where its host star is one of three stars that are gravitationally bound in a trinary system.

Although it is too hot to support life, its similarity to our home planet marks it as an Earth analog. This means that its proximity to the Earth can be used in studying the evolution of planets and in understanding the differences between each Earth-like world.

LTT 1445 Ac was first identified in 2021 using data collected by the Transiting Exoplanet Survey Satellite (TESS) telescope. However, astronomers encountered some difficulties in observing this planet which made it hard for them to investigate its properties.

Astronomers find and study exoplanets by looking for changes in the light of the host star. In systems of stars, the stellar companions can also affect the light of the other stars. So even if LTT 1445 Ac is only 22 light-years away, it is actually a pretty tiny thing to try and look at.

In understanding the properties of an exoplanet, two types of measurement are required. The first type is called transit data which refer to the tiny drips in starlight that occur as an exoplanet passes between the Earth and the star. The second is radial velocity data which measures the amount of gravity exerted by the exoplanet on the star.

TESS detects planets by using the transit method. Unfortunately, its data on LTT 1445 Ac was poorly resolved which makes it hard to determine if the dimming was the result of an entire exoplanet eclipsing the starlight, or just part of a planet that 'grazes' the sun's disc.

Using radial velocity data, the presence of the exoplanet was confirmed. But in order to gain a better understanding of the properties of this Earth-like world, a higher resolution transit data was needed.

Better View With Hubble

A team of NASA scientists used the Hubble Space Telescope to get better insight into the properties of LTT 1445 Ac. Led by astrophysicist Emily Pass of the Harvard & Smithsonian Center for Astrophysics, they used Hubble's Wide Field Camera 3 to take observations of the LTT 1445 system.

Using the data about the planet's radius and mass, the experts were able to determine that this world has a density of 5.9 grams per cubic centimeter. Earth has a density of 5.51 grams per cubic centimeter, which means that the exoplanet is very close to Earth in terms of size and composition.

The exoplanet's host star is a red dwarf, which is cooler and dimmer than our own Sun. However, LTT 1445 Ac has an orbital period of just 3.12 days, which means that its temperature is around 500 degrees Fahrenheit (260 degrees Celsius) on average.