A spaceflight era closes with end of Dawn and Kepler missions
The Kepler Space Telescope and the Dawn mission to Ceres and Vesta both lasted approximately a decade and yielded groundbreaking data about habitability, stellar systems, and the search for life beyond Earth. Within just weeks of one another, both spacecraft ran out of fuel, marking the end of an era that transformed our understanding of both our solar system and others.
Kepler, which launched in 2009, discovered 2,600 of the 4,000 confirmed exoplanets currently known. Some of these include rocky planets in their stars’ habitable zones, where temperatures allow liquid water to exist on their surfaces. An entirely new class of planets not present in our solar system, super-Earths with sizes between those of Earth and Neptune, is one of Kepler’s most significant discoveries.
Significantly, the mission revealed that Earth-sized planets are common, a fact not known at launch.
Dawn marked several firsts in robotic space exploration, including the first spacecraft to orbit two separate objects, the first to orbit any object in the asteroid belt between Mars and Jupiter, and the first science mission to use ion propulsion, a technology that gave the spacecraft additional velocity and enabled it to orbit Vesta, then depart, travel to Ceres and enter orbit around the dwarf planet.
Scientists were surprised by evidence that Ceres could be geologically active, has chemistry that could support life, and may harbor a subsurface ocean or may have harbored one in its past. This puts the dwarf planet in the growing category of ocean worlds being discovered in our solar system that could potentially host microbial life. Other such worlds include Jupiter’s moon Europa, Saturn’s moons Titan and Enceladus, Pluto, and possibly Neptune’s moon Triton.
Both missions can be described as having put scientists a step closer in the search for extraterrestrial life, and data sets from both will continue to provide scientists with discoveries for many years.
The search for exoplanets has already been taken up by the Transiting Exoplanet Survey Satellite (TESS), which launched in April of this year (2018). TESS is searching the 200,000 brightest stars closest to Earth. The James Webb Space Telescope (JWST), whose launch has been delayed to 2021, will be capable of studying the atmospheres of planets discovered by TESS and identifying their chemical compositions.
Between 20 and 50 percent of the stars visible in the night sky likely have rocky Earth-sized planets orbiting in their habitable zones, Kepler found.
Unlike Kepler, Dawn does not have an immediate successor to study Ceres, Vesta, or any other large objects in the main asteroid belt.
“In many ways, Dawn’s legacy is just beginning. Dawn’s data sets will be deeply mined by scientists working on how planets grow and differentiate, and when and where life could have formed in our solar system. Ceres and Vesta are important to the study of distant planetary systems, too, as they provide a glimpse of the conditions that may exist around young stars,”said mission principal investigator Carol Raymond of NASA’s Jet Propulsion Laboratory (JPL) in a NASA news release.
Two other missions missions to the asteroid belt are underway. The Japanese Aerospace Exploration Agency’s (JAXA) Hayabusa2 entered orbit around the half-mile-wide asteroid Ryugu this summer and will eventually land on its surface to collect samples for return to Earth. NASA’s OSIRIS-REx spacecraft is on course for entering orbit around the asteroid Bennu, where it will search for ices and deposits of volatiles. This mission will also land on the asteroid’s surface and collect samples that will be returned to Earth for analysis.
Efforts to better understand rocky planets continue on Mars, where the InSight lander, which will probe the planet’s deep interior, will touch down on Nov. 26. In two years, the Mars 2020 rover will arrive and conduct new geological tests for evidence of ancient life and determine whether the environment it lands in could be habitable for life.
The potentially groundbreaking Europa Clipper is set to conduct a detailed study of Europa’s habitability during the 2020s. Its nine science instruments will search for eruptions of water at or near the moon’s surface and look for water plumes observed by the Hubble Space Telescope (HST) that could be connected to a subsurface ocean.
Video courtesy of NASA / Jet Propulsion Laboratory
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.