Scientists in the United States have confirmed the existence of a tiny world orbiting a small red dwarf star just 22 light-years away, marking it as the closest known Earth-sized exoplanet to our Solar System. Named LTT 1445 Ac, this exoplanet is approximately 1.37 times the mass and 1.07 times the radius of Earth. Although it is too hot to support life, its similarity to our own planet makes it an Earth analog and an excellent candidate for studying planetary evolution and the factors that contribute to the differences between Earth-like worlds. Initially identified using data from the TESS exoplanet-hunting telescope in 2021, observing this exoplanet presented challenges due to the unique trinary system it resides in. The star LTT 1445 Ac orbits is part of a gravitational trio, where the presence of other stars within the system affects the light observed from each of them.
Despite its relatively close proximity, observing an Earth-sized exoplanet presents unique difficulties. To determine the properties of an exoplanet, two types of measurements are required. Transit data involves identifying the tiny dips in starlight that occur when the exoplanet passes between its host star and the observer. Radial velocity data is another measurement method that records changes in the wavelength of starlight caused by the exoplanet’s gravitational pull on the star. By combining the transit data for an exoplanet’s radius and the radial velocity data for its mass, scientists can calculate its density and infer its composition. A low density suggests an exoplanet with a primarily gaseous atmosphere, similar to a gas giant, while a higher density indicates a rocky composition akin to Earth, Venus, Mars, or Mercury. In the case of LTT 1445 Ac, the transit data obtained from the TESS mission was insufficiently detailed to confirm its properties. Instead, radial velocity data was used for the initial confirmation of its existence.
To gain a more comprehensive understanding of the exoplanet’s properties, higher-resolution transit data was required. This is where the Hubble Space Telescope became an invaluable tool. A team led by astrophysicist Emily Pass from the Harvard & Smithsonian Center for Astrophysics utilized Hubble’s Wide Field Camera 3 to observe the LTT 1445 system and search for transits of LTT 1445 Ac. Despite the interference caused by the interaction between the three stars in the trinary system, the team managed to capture the exoplanet passing in front of its host star. This breakthrough allowed Pass and her colleagues to obtain a high-resolution measurement of LTT 1445 Ac’s diameter. Combining this data with the exoplanet’s mass, they determined that it has a density of 5.9 grams per cubic centimeter, indicating a rocky composition analogous to Earth.
While LTT 1445 Ac shares similarities in size and composition with Earth, its hostile environment makes it unlikely to support life as we know it. Orbiting a red dwarf star, which is cooler and dimmer than our Sun, this exoplanet has an incredibly short orbital period of just 3.12 days. Consequently, its surface temperature reaches a scorching 260 degrees Celsius (500 degrees Fahrenheit). However, the ability to obtain clear transit data provides scientists with the opportunity to study its atmosphere in the future. By characterizing this exoplanet further, researchers can gain insights into the formation and evolution of Earth-like worlds in different system architectures. Additionally, this knowledge contributes to our understanding of the potential emergence of life elsewhere in the galaxy. Scientists are particularly excited about the prospect of using spectroscopy to analyze the exoplanet’s atmosphere, not only with Hubble but also with the upcoming James Webb Space Telescope.
LTT 1445 Ac stands as the closest known Earth-sized exoplanet to our Solar System. Despite its extreme conditions, the similarities it shares with our planet make it an exciting subject of study for scientists. By exploring and understanding this exoplanet in greater detail, researchers can expand our knowledge of the formation and evolution of Earth-like worlds within the vast expanse of the universe. Furthermore, the proximity of LTT 1445 Ac offers hope for future discoveries and potential breakthroughs in our ongoing quest to uncover the existence of extraterrestrial life.