Exploring Comets and Asteroids: Time Capsules of the Solar system

On Nov. 12, 2014, space history was made with the first soft landing of a spacecraft on a comet. Following a 10-year chase, the European Space Agency’s Rosetta spacecraft had rendezvoused with comet 67P/Churyumov-Gerasimenko, sending its Philae lander down to the surface, where it will begin conducting science.

The Philae lander of the European Space Agency’s Rosetta mission is safely on the surface of Comet 67P/Churyumov-Gerasimenko, as these first two images from the lander’s CIVA camera confirm. One of the lander’s three feet can be seen in the foreground. The view is a two-image mosaic taken on Nov. 12
Image Credit:

The historic landing came on the heels of another once-in-a-lifetime opportunity when, in October 2014, multiple Mars missions and the Hubble Space Telescope captured spectacular images of comet C/2013 A1 Siding Spring as it made a close approach to the Red Planet, much closer than any other known comet flyby of Mars or Earth.

Small bodies like comets and asteroids are “time capsules” that contain information about the history of our solar system, making them particularly interesting targets of study by scientists. Missions like Rosetta help advance spaceflight capabilities that are putting more of these bodies within our reach—especially those that travel close to Earth—opening new possibilities for exploration. As NASA looks ahead to multiple robotic and human missions over the next decade that will collect samples from asteroids, the agency will build on what we learn from missions like Rosetta to further advance capabilities needed to navigate around these small bodies objects, map and directly interact with their surfaces, and study them in depth.

Comets and asteroids are debris left over from the formation of planets and moons. These small bodies orbit the sun along with all the other bodies in the solar system. Comets are located in the Kuiper Belt and the Oort Cloud, the outermost regions of the Solar system. Most asteroids are located in a belt between Mars and Jupiter. Occasionally gravitational disturbances cause comets and asteroids to change their orbital paths, sometimes bringing them near a planet. A near-Earth object (NEO) is one that comes within 50 million kilometers (31 million miles) of our planet.

Craters on planets and moons in the solar system are evidence of a long history of impacts with asteroids and comets. For the first billion years of Earth’s existence, comet and asteroid impacts rendered Earth’s surface too hot to allow the existence of sufficient quantities of water and carbon-based molecules for life. Life on Earth began at the end of this period, some 3.8 billion years ago.

By observing, tracking and characterizing NEOs, scientists can learn more about their composition. Further studies of these objects could help determine how the building blocks of life, and life itself, originated on Earth.

Asteroids and comets that stray close to Earth are of special interest to scientists because they could hold clues to the origins of life on Earth. These objects are possible targets for spacecraft missions.

Three new missions will return samples of asteroids to Earth for future study. Later this year, the Japan Aerospace Exploration Agency (JAXA) will launch its Hayabusa-2 mission, which will robotically collect samples of asteroid 1999JU3 in 2018 and return them to Earth in 2020. The mission builds on the legacy of JAXA’s Hayabusa mission, which explored asteroid Itokawa and returned samples to Earth in 2010.

In 2016 NASA will launch its robotic asteroid sample return mission, the Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer (OSIRIS-Rex). The mission will rendezvous with asteroid 1999 RQ36, also known as “Bennu,” in 2019, take samples and bring them back to Earth, arriving in 2023. Key objectives for the mission include finding answers to basic questions about the composition of the very early solar system and the source of organic materials and water that made life possible on Earth.

Hayabusa-2 and OSIRIS-REx could help NASA choose its target for the first-ever mission to capture and redirect an asteroid. NASA’s Asteroid Redirect Mission (ARM) in the 2020s will help NASA test new technologies needed for future human missions to Mars. For the ARM mission, NASA plans to launch a robotic spacecraft to first rendezvous with a near Earth asteroid. The agency is now weighing two concepts for what the spacecraft does next —one would fully capture a small asteroid about 5-10 meters (15-30 feet) in size, using an inflatable mechanism, and the other would retrieve a boulder about 2-5 meters (6 to 15 feet) in size from a much larger asteroid using a robotic arm. The spacecraft will then use the gentle thrust of its solar electric propulsion system and the gravity field of the Earth and Moon to redirect the asteroid into a stable orbit around the Moon, where astronauts will explore it in the mid-2020s, returning to Earth with samples.

Scientists studying samples of asteroids and comets already on Earth continue to make exciting discoveries, like the possible detection of interstellar particles in a comet sample returned by NASA’s Stardust mission. Data from other comet and asteroid missions, like NEAR Shoemaker, Deep Impact and EPOXI, remain valuable resources for scientists planning future missions and refining models of comet and asteroid characteristics.

Follow the latest missions and discoveries at NASA’s Asteroid and Comet Watch.