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Planetary Sciences

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Small Planetary Bodies
Small Planetary Bodies

Studies involving small planetary bodies and near earth objects involve astronomy, and geology, modeling activities. Researchers in the field conduct those activities to learn about how planets form and also to identify objects in close proximity to earth. JPL has sponsored many programs to identify small planetary bodies and to support NASA missions.

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.

Researchers in the small bodies area study observational planetary astronomy, planetary geology, data analysis and interpretation, theoretical modeling, and mission leadership and support. In addition, small planetary bodies research involves maintaining and exporting the past, current and future positions for each of the 8 planets in the Solar System, 170 natural satellites and hundreds of thousands of comets and asteroids, through the Solar System Dynamics Group. This group’s Horizons Ephemeris Export System has provided more than 18 million predictions for solar system object positions to an international community of scientists.

Selected Mission Projects and Research Efforts

Typical missions to asteroids and comets include the following types of instruments:
  • Imager
  • IR Spectrometer and UV Spectrometer
  • Lidar
  • X-Ray Spectrometer, Gamma Ray Spectrometer, Alpha/X-ray Spectrometer
  • Impact dust mass spectrometer
  • Magnetometer
  • Plasma Package

The members of the group have played key leadership roles for many missions, including Voyager, Cassini-Huygens, Deep Space 1, Stardust, and the Mars Exploration Rover, and many of its observers have obtained ground-based measurements in support of these and other NASA missions.

Near Earth Object Program

JPL’s Near Earth Object Program is responsible for tracking the motions of comets and asteroids that can closely approach the Earth. In 2009 alone, NASA-supported near-Earth object telescopic observers have discovered more than 782 of these objects. The Program Office continuously monitors their motions by improving their orbits, identifying future Earth close approaches and, for those objects of particular interest, computing Earth impact probabilities.

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 with embedded dust particles, comets originally formed in the cold outer planetary 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 their status as the relatively unchanged remnant debris from the solar system formation process some 4.6 billion years ago.

known NEOs
Near earth asteroid discoveries by the NEO program at JPL since 1995.

Deep Impact

Map of comet Temple 1
Composite image of Comet Tempel 1, with data from Deep Impact's three cameras. Arrows a and b point to large, smooth regions. The impact site is indicated by the third large arrow. The scale bar is 1 km and the two arrows above the nucleus point to the sun and the rotational axis of the nucleus.

The Deep Impact mission was launched in January, 2005 and encountered Comet Tempel 1 in July, 2005. The impacting spacecraft separated from the mother spacecraft about 24 hours in advance of the encounter and successfully collided with the cometary nucleus as the mother spacecraft flew past and observed the impact phenomena. The Deep Impact mission successfully carried out its science objectives. The combination of imaging, spectroscopic observations and the observed ejecta from the spacecraft impactor established the following results: (1) The nucleus was determined to have the longest/shortest dimensions of 7.6 and 4.9 kilometers (2) The nucleus is underdense and very porous with a bulk density of about 0.4 grams per cubic centimeter and a porosity of about 70% (3) the strength of the surface material is very weak – less than fractured ice (4) the nucleus is chemically heterogeneous with the carbon dioxide to water ratio varying by a factor of 4 from north to south (5) there is very little in the way of surface ices with most of the water ice lying about a meter below the surface layer of dust (6) relatively pure and tiny ice grains were evident in the ejecta (7) there appears to be substantial evidence for structural nucleus layering with relatively young smooth regions adjacent to relatively old and cratered regions.

Having completed its mission at comet Tempel 1 in 2005, the Deep Impact mother spacecraft continued on and with the help of some trajectory modifications using Earth swingbys, it will fly closely past comet Hartley 2 on November 4, 2010. Comet Hartley 2 is a comet that is both smaller and more active than comet Tempel 1. It will provide an interesting contrast to the comet Tempel 1 results.


The Japanese Hayabusa spacecraft, launched in 2003, spent a successful few months in rendezvous with near-Earth asteroid Itokawa in the fall of 2005, returned to the Earth’s neighborhood in 2010 and parachuted a surface sample capsule onto the Australian outback on June 13, 2010. This is a Japanese led project with significant U.S. involvement on the spacecraft navigation and science teams. The U.S. Project Manager and Project Scientist are located at JPL. Although the sample collection technique at the asteroid did not go as planned, the spacecraft did touch down on the surface of Itokawa more than twice in late 2005 and the hope is that some surface particles were captured by the spacecraft. In the summer and fall of 2010, sample scientists in Japan have been carefully examining the few tiny particles that are evident in the sample capsule. While spending a few months in close proximity to Itokawa, the following results were established via the instrumentation on board the Hayabusa spacecraft: (1) the dimensions of Itokawa are 535 x 294 x 209 meters (2) the bulk density and porosity were determined to be 1.9 grams per cubic centimeter and 40% respectively (3) its rotation period is 12.1 hours (4) its albedo, or reflectivity, is 25 to 30 % (5) it mineralogy is consistent with an olivine rich, ordinary chondrite meteorite type (6) the structure is bimodal and very rough suggesting that a long ago asteroid impact resulted in a re-agglomerated ruble pile structure for Itokawa (7) no satellites or ring of dust were evident in the imaging data.


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