Asteroids, Comets, and Small Satellites

Rosetta target comet
The Rosetta target comet 67P/Churyumov-Gerasimenko, observed with the FORS2 instrument at the 8.2m Antu telescope of the Very Large Telescope Observatory VLT of the European Southern Observatory ESO at Cerro Paranal in Chile.

Small planetary body researchers at JPL study asteroids, comets, Kuiper Belt Objects (KBOs) and icy moons, using observations at ground-based telescopes, investigations in planetary geology, data analysis and interpretation, and theoretical modeling, while providing mission leadership and support.  In addition, this field involves maintaining and exporting the past, current, and future positions for each of the eight planets in the Solar System, 181 natural satellites, and hundreds of thousands of comets, asteroids, and KBOs through the Solar System Dynamics Group. This group’s Horizons Ephemeris Export System has provided more than 190 million predictions from over one million different computers for Solar System object positions to an international community of scientists.


Selected Mission Projects and Research Efforts


Typical missions to asteroids, comets, moons, and KBOs include the following types of instruments:

  • Imaging system
  • IR Spectrometer and UV Spectrometer
  • Lidar
  • X-Ray Spectrometer, Gamma Ray Spectrometer, Alpha/X-ray Spectrometer
  • Impact dust mass spectrometer
  • Magnetometer
  • Plasma Package

JPL small body investigators have played key leadership roles for many missions, including Voyager, Cassini-Huygens, Deep Space 1, Stardust, New Horizons, Near Earth Asteroid Rendezvous, Rosetta, Dawn, Hayabusa-1, Deep Impact, EPOXI, WISE, and NEOWISE.  Many JPL researchers have obtained ground-based measurements in support of these and other NASA missions using assets such as the Palomar Mountain telescopes, NASA’s Infrared Telescope Facility, the Arecibo and Goldstone radio telescopes, and JPL’s Table Mountain Observatory.


Near Earth Object Program

NEOs Discovered Chart
Near-Earth asteroid discoveries tabulated by the NEO program at JPL since 1995.

Near-Earth Objects (NEOs) are comets and asteroids that have been nudged by the gravitational attraction of nearby planets into orbits that allow them to enter the Earth's neighborhood. Composed mostly of water ice and embedded dust particles, comets originally formed in the cold outer Solar System while most of the rocky asteroids formed in the warmer inner Solar System between the orbits of Mars and Jupiter. The scientific interest in comets and asteroids is due largely to the fact that they form the relatively unchanged remnant debris from the Solar System formation process some 4.6 billion years ago.

JPL’s Near-Earth Object Program is responsible for tracking the motions of NEOs that closely approach the Earth. In 2015 alone, near-Earth object telescopic observers supported by NASA have discovered more than 1,566 of these objects. The NEO Program Office continuously monitors the motions of these objects by improving knowledge of their orbits, identifying future Earth close approaches and, for objects of particular interest, computing Earth impact probabilities.


Radar Studies

Using the Arecibo Radio Telescope in Puerto Rico and the Deep Space Network, JPL manages one of the leading research programs in radar studies of NEOs. The aim is to understand the formation, evolution, morphology, composition, and dynamical properties of NEOs. These studies help describe the early conditions in the solar nebula and formation of the planets. Results of these studies also help characterize potential targets for future NASA missions. 



Images of Vesta and Ceres
Dawn Framing Camera Images of the South Pole of Vesta (left) and the bright evaporate deposits on Ceres (right).

Dawn is the first mission to study Main Belt asteroids in great detail. The mission’s investigations have centered around two of the three protoplanets among the asteroids -- the rocky 4 Vesta and the carbonaceous, aqueously altered 1 Ceres. Launched in 2007, Dawn entered orbit around 4 Vesta in 2011 for a 14-month mission. The main goals of the investigation at Vesta were to characterize the geology and composition of the asteroid, and to understand its connections to the largest group of terrestrial meteorites, the basaltic achondrites. To this end, Dawn characterized a large impact basin at the South Pole of Vesta, the likely source of the meteorites. After a successful tour, Dawn left Vesta for a cruise trajectory and entered orbit around 1 Ceres in late 2012. Dawn discovered evaporate deposits in the floor of a large crater, suggesting that liquid may lie underneath its surface. Dawn will remain in orbit around Ceres. 



An artist’s conception of the NEOWISE spacecraft in orbit about the Earth. 

The Wide-field Infrared Survey Explorer (WISE) was a NASA telescope in a sun-synchronous orbit that ran out of its coolant, as planned, in October 2010. Prior to being put into hibernation in 2011, WISE conducted a program of searching for and characterizing NEOs.  In August 2013, it was refurbished as a new mission, dubbed NEOWISE, with a dedicated goal of finding and studying NEOs. As of the beginning of 2016, WISE and NEOWISE have discovered 230 NEOs, 40 of which are Potentially Hazardous Objects that approach to within 0.05 AUs of Earth and are sufficiently large (~100 m in diameter) to cause massive devastation on the Earth should they impact. Twenty-five comets were also discovered. One of the major scientific results of the mission was that low-albedo carbonaceous asteroids are far more common among the NEO population than previously thought. 



Comet 67P
A close-up image of Comet 67P, showing its layered structure and boulders.

Rosetta is a European Space Agency mission to closely study and characterize Comet 67P/Churyumov-Gerassimenko through a perihelion passage. NASA contributed three instruments to the mission: the Microwave Instrument for the Rosetta Mission (MIRO), built and managed at JPL, the Alice ultraviolet spectrometer, and the Ion Electron Spectrometer (IES). JPL manages the NASA contributions to the Rosetta mission. In addition, numerous NASA-funded US Co-Investigators contributed to the European instruments on Rosetta.

Rosetta was launched in 2004, and rendezvoused with the comet in August 2014 for a detailed study of its nucleus, dust and ion coma, and its interaction with the solar wind. Its Philae probe was jettisoned from the spacecraft on November 12, 2014 in order to land on the surface of the comet. The lander’s instruments returned data for two days. Among the unexpected discoveries at the comet were molecular oxygen, a patchy distribution of water ice at its surface, a far more complex surface with cliffs, outgassing-pits, boulders, and a layered structure. Comet 67P is a nearly binary object, likely formed from two planetesimals.