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Sedna Mystery Deepens as Hubble Offers Best Look at Farthest Planetoid

This is the clearest-ever view of the farthest object yet discovered in the solar system. The object is unofficially named "Sedna" (after an Inuit goddess of the sea).
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At a distance of over 8 billion miles, Sedna is so far away it is reduced to one picture element (pixel) in this image, taken in high-resolution mode with Hubble's Advanced Camera for Surveys. This image sets an upper limit on Sedna's size of 1,000 miles in diameter. It is surprising that Hubble does not see a suspected moon near the planetoid. Either the moon's not there, or, far less likely, it is being eclipsed by Sedna, or it is transiting Sedna. The gravitational tug of a moon would best explain Sedna's extremely slow rotation of between 20-50 days, as inferred from ground-based photometric observations.
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Hubble took a total of 35 images of Sedna on March 16, 2004. The planetoid appeared to move slightly between exposures, due to the motion of Hubble around Earth and the motion of the Earth around the Sun. Sedna, too, is moving through space, but too slowly for that to be seen in these images. The fact that the object shows this parallax shift between exposures demonstrates that Sedna is a member of the solar system, and hence is far closer to the Earth than the background star (at right) in the same field of view.
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A plot of Sedna's apparent motion through space from 2003 to 2005 easily demonstrates that it is close enough to be part of the solar system. The looping path isn't real, but is caused by the fact that Earth is orbiting the Sun and so "laps" Sedna, like a faster race car, once every year. This gives the illusion that Sedna is briefly moving backward along its orbit. Called retrograde motion, this projection effect was noted by the ancient Greeks as they plotted the periodic backward motion of nearby Mars.
About the Object
- R.A. PositionR.A. PositionRight ascension – analogous to longitude – is one component of an object's position.03h 13m 51.12s
- Dec. PositionDec. PositionDeclination – analogous to latitude – is one component of an object's position.05° 45' 41.14"
- DistanceDistanceThe physical distance from Earth to the astronomical object. Distances within our solar system are usually measured in Astronomical Units (AU). Distances between stars are usually measured in light-years. Interstellar distances can also be measured in parsecs.Approximately 13.5 billion kilometers (8.4 billion miles)
About the Data
- Data DescriptionData DescriptionProposal: A description of the observations, their scientific justification, and the links to the data available in the science archive.
Science Team: The astronomers who planned the observations and analyzed the data. "PI" refers to the Principal Investigator.This data are taken from HST proposal 10041: M. Brown (Caltech). The science team includes: M. Brown (Caltech), C. Trujillo (Gemini Observatory, Hawaii), and D. Rabinowitz (Yale University). - InstrumentInstrumentThe science instrument used to produce the data.HST>ACS/HRC
- Exposure DatesExposure DatesThe date(s) that the telescope made its observations and the total exposure time.March 16, 2004, Exposure Time: 1.1 hours
- FiltersFiltersThe camera filters that were used in the science observations.F435W (B)
- Object NameObject NameA name or catalog number that astronomers use to identify an astronomical object.2003 VB12, Sedna, K31114A
- Release DateApril 14, 2004
- Science ReleaseHubble Observes Planetoid Sedna, Mystery Deepens
- Credits
Related Images & Videos
Long View from a Lonely Planet
This is an artist's impression of noontime on Sedna, the farthest known planetoid from the Sun. Over 8 billion miles away, the Sun is reduced to a brilliant pinpoint of light that is 100 times brighter than the full Moon. (The Sun would actually be the angular size of Saturn as...
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Claire Andreoli
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
claire.andreoli@nasa.gov