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News Release Archive:

News Release 469 of 967

April 14, 2004 01:00 PM (EDT)

News Release Number: STScI-2004-14

Hubble Observes Planetoid Sedna, Mystery Deepens

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Image: Sedna Mystery Deepens as Hubble Offers Best Look at Farthest Planetoid

Sedna Mystery Deepens as Hubble Offers Best Look at Farthest PlanetoidSTScI-PRC2004-14a

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ABOUT THIS IMAGE:

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).

[Lower right]

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.

[Lower left]

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.

[Top]

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.

Object Names: 2003 VB12, Sedna, K31114A

Image Type: Astronomical/Illustration

Credit: NASA, ESA and M. Brown (Caltech)

NEWS RELEASE IMAGES

The above montage includes these images:

Plot of Planetoid Sedna's Apparent Motion through Space from 2003 to 2005 Image Type: Astronomical Plot of Planetoid Sedna's Apparent Motion through Space from 2003 to 2005 Parallax Shift Shows Planetoid Sedna is Part of Solar System Image Type: Astronomical Parallax Shift Shows Planetoid Sedna is Part of Solar System HST/ACS Co-added Image of Sedna - March 16, 2004 Image Type: Astronomical HST/ACS Co-added Image of Sedna - March 16, 2004

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