Discover the secrets of a nearby Earth-sized world

Hubble telescope confirms its Earth-like size Exoplanet LTT 1445Ac, provides new insights into its composition and the potential for further atmospheric studies.

Many planets around nearby stars cannot be seen directly. Instead, they are found when they temporarily pass in front of their parent star, an event called a transit. During the transit, they block a little light from the star, casting shadows for Earth observers.

Astronomers learn a lot from these fleeting events. They can measure a planet’s orbital period, study its atmosphere, and estimate its size. The tricky thing is that the planet may only touch the edge of the star during the transit, giving an inaccurate measurement of its diameter.

One of these nearby exoplanets, LTT 1445Ac, located just 22 light-years away, was first identified by NASATransiting Exoplanet Survey Satellite (he-goat). But TESS does not have the optical resolution required to precisely determine a planet’s diameter by refining its path across the face of the star.

Hubble, with his sharp vision, accurately measured the diameter of the planet to be only 1.07 times the diameter of the Earth. This makes it the Earth’s cousin in size. But that’s where all the similarity ends. LTT 1445Ac is too close to the red dwarf sun to be habitable. Surface temperatures are around 500 degrees F – Temperatures inside the pizza oven.

This is an artist’s rendering of the nearby Earth-sized exoplanet LTT 1445Ac. The planet orbits a red dwarf star. The star is located in a triple system, with two closely orbiting red dwarfs at the top right. The black dot in front of the bright red sphere in the center of the image is the planet LTT 1445Ac crossing the face of the star. The planet’s surface temperature is about 500 degrees Fahrenheit. In the lower left foreground is another planet in the system, LTT 1445Ab. This scene was captured 22 light-years away, looking back toward our Sun, the bright spot on the lower right. Some background stars are part of the Boötes constellation. Image credit: NASA, ESA, Leah Hostak (STScI)

The Hubble Space Telescope measures the size of the closest Earth-sized transiting planet

NASA’s Hubble Space Telescope has measured the size of the closest Earth-sized exoplanet passing through the face of a nearby star. This alignment, called a transit, opens the door for later studies to see what kind of atmosphere, if any, might exist in the rocky world.

The minor planet, LTT 1445Ac, was first discovered by NASA’s Transiting Exoplanet Survey Satellite (TESS) in 2022. However, the geometry of the planet’s orbital plane relative to its star as seen from Earth was uncertain because TESS does not have the required optical resolution . . This means that detection can be so-called Grazing crossing, where the planet passes through only a small part of the disk of the parent star. This would lead to an inaccurate minimum diameter of the planet.

“There was a possibility that this system had unlucky geometry, and if so, we would not have measured the correct size. But thanks to Hubble’s capabilities we were able to determine its diameter,” says Emily Bass of the Center for Astrophysics at Harvard and Smithsonian in Cambridge, Massachusetts.

Hubble’s observations show that the planet makes a completely normal transit through the star’s disk, resulting in a true size of only 1.07 times Earth’s diameter. This means that the planet is a rocky world, like Earth, with roughly the same surface gravity. But at a surface temperature of about 500 degrees Fahrenheit, it’s too hot for life as we know it.

This chart compares two scenarios for how an Earth-sized exoplanet might pass in front of its host star. The lower path shows the planet patronizing the star. Studying the light from such a transit could lead to an inaccurate estimate of the planet’s size, making it appear smaller than it actually is. The upper path shows perfect geometry, with the planet crossing the entire disk of the star. The Hubble Space Telescope’s resolution can distinguish between these two scenarios, resulting in an accurate measurement of the planet’s diameter. Image credit: NASA, ESA, Elizabeth Wheatley (STScI)

The planet orbits the star LTT 1445A, which is part of a triple system of three red dwarf stars located 22 light-years away in the River constellation. The star has two other reported planets larger than LTT 1445Ac. A tight pair of two other dwarf stars, LTT 1445B and C, lies about 3 billion miles away from LTT 1445A, which was also identified by Hubble. The alignment of the three stars and the sideways orbit of the BC pair indicate that everything in the system is co-planar, including the known planets.

“Transiting planets are interesting because we can describe their atmospheres using spectroscopy, not only with the Hubble telescope but also with the James Webb Space Telescope. Our measurements are important because they tell us that this is likely to be a very close terrestrial planet. We are looking forward to “Follow-up observations will allow us to better understand the diversity of planets around other stars.”

This research was published in Astronomical magazine.

Reference: “The HST/WFC3 light curve supports the terrestrial composition of the closest exoplanet to transit an M dwarf” by Emily K. Bass, Jennifer J. Winters, David Charbonneau, Aurelia Balkansky, Nicole Lewis, Maura Lally, Jacob L. Bean, Ryan Cloutier, and Jason D. Eastman, September 25, 2023, Astronomical magazine.
doi: 10.3847/1538-3881/acf561

the Hubble Space Telescope It is an international cooperation project between NASA and the European Space Agency. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, operates the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts science operations on the Hubble Telescope. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, DC