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DE400 (and DE403, DE405, DE406 etc.) are designations for the more recent members of a series of astronomical ephemerides produced by numerical integration at the Jet Propulsion Laboratory. ('JPL DE' stands for Jet Propulsion Laboratory Development Ephemeris.) The ephemerides of the DE4xx series are expressed in coordinates referred to the ICRF (International Celestial Reference Frame). These ephemerides provide rectangular (solar-system barycentric) coordinates of position and velocity for the Earth-Moon barycenter, Sun and eight major planets, and geocentric coordinates of the Moon. These data enable derivation of geocentric or heliocentric coordinates of relevant bodies. From the issue for 2003 onwards, the Astronomical Almanac has been based on JPL ephemeris DE405.[1] The DE4xx series of ephemerides is an update to the DE200 ephemeris.[2]
The data have been made publicly available,[3] in the form of data files containing Chebyshev coefficients, along with source codes for access and basic data-processing to recover positions and velocities, thus amounting to software packages that provide a means of re-generating the positions and velocities of the underlying respective JPL Planetary and Lunar Ephemerides.[4]
Evaluation and interpolation of the Chebyshev polynomials can give planetary and lunar coordinates to high precision. DE405 accuracy for the inner planets is about 0.001 arcseconds (equivalent to about 1 km at the distance of Mars); for the outer planets it is generally about 0.1 arcseconds. The 'reduced accuracy' DE406 ephemeris gives an interpolating accuracy (relative to the full ephemeris values) no worse than 25 metres for any planet and no worse than 1 metre for the moon.
Documentation for later JPL ephemerides points out the availability of (independently produced) C and Java interpolating routines.
Nevertheless, the documentation indicates that the ephemerides in this form are not intended for a casual user. They are available for download by anonymous FTP.[5]
DE402 was released in 1995, and was quickly superseded by DE403.
DE403[6] was released in 1995. For the first time, the JPL ephemeris was expressed in the coordinates of the International Earth Rotation Service (IERS) reference frame, essentially the ICRF. The data crunched by JPL to derive the ephemeris began to move away from limited-accuracy telescopic observations and more toward higher-accuracy radar-ranging of the planets, radio-ranging of spacecraft,[7] and very-long-baseline-interferometric (VLBI) observations of spacecraft, especially for the four inner planets. Telescopic observations remained important for the outer planets because of their distance, hence the inability to bounce radar off of them, and the difficulty of parking a spacecraft near them. The perturbations of 300 asteroids were included, vs DE118/DE200 which included only the five asteroids determined to cause the largest perturbations. Better values of the planets' masses had been found since DE118/DE200, further refining the perturbations. Lunar Laser Ranging accuracy was improved, giving better positions of the Moon. DE403 covered the time span Apr 1599 to Jun 2199.[8]
DE404[9] was released in 1996. A so-called Long Ephemeris, this condensed version of DE403 covered 3000 BC to 3000 AD. While both DE403 and DE404 were integrated over the same timespan, the interpolation of DE404 was somewhat reduced in accuracy and nutation of the Earth and libration of the Moon were not included.
DE405[10] was released in 1998. It added several years' extra data from telescopic, radar, spacecraft, and VLBI observations (of the Galileo spacecraft at Jupiter, in particular). The method of modeling the asteroids' perturbations was improved, although the same number of asteroids were modeled. The ephemeris was more accurately oriented onto the ICRF. DE405 covered 1600 to 2200 to full precision.
DE406 was released with DE405 in 1998. A Long Ephemeris, this was the condensed version of DE405, covering 3000 BC to 3000 AD with the same limitations as DE404.
DE407[11] was apparently unreleased. Details in readily-available sources are sketchy.
DE408[12] was an unreleased ephemeris, created in 2005 as a longer version of DE406, covering 20,000 years.
DE409[13] was released in 2003 for the MER spacecraft arrival at Mars and the Cassini arrival at Saturn. Further spacecraft ranging and VLBI (to the Mars Global Surveyor, Mars Pathfinder and the Mars Odyssey spacecraft) and telescopic data were included in the fit. The orbits of the Pioneer and Voyager spacecraft were reprocessed to give data points for Saturn. These resulted in improvements over DE405, especially to the predicted positions of Mars and Saturn. DE409 covered the years 1901 to 2019.