Hubble Observes Planetoid Sedna, Mystery Deepens

April 14, 2004 01:00 PM (EDT)

Astronomers poring over 35 NASA Hubble Space Telescope images of the solar system’s farthest known object, unofficially named Sedna, are surprised that the object does not appear to have a companion moon of any substantial size.

This unexpected result might offer new clues to the origin and evolution of objects on the far edge of the solar system.

When Sedna’s existence was announced on March 15, its discoverer, Mike Brown of Caltech, was so convinced it had a satellite that an artist’s concept of Sedna released to the media included a hypothetical moon.

Brown’s prediction was based on the fact that Sedna appears to have a very slow rotation that could best be explained by the gravitational tug of a companion object. Almost all other solitary bodies in the solar system complete a spin in a matter of hours.

“I’m completely baffled at the absence of a moon,” says Brown. “This is outside the realm of expectation and makes Sedna even more interesting. But I simply don’t know what it means.”

Immediately following the announcement of the discovery of Sedna, astronomers turned the Hubble Space Telescope toward the new planetoid to search for the expected companion moon. The space-based platform provides the resolving power needed to make such precision measurements in visible light. “Sedna’s image isn’t stable enough in ground-based telescopes,” says Brown.

Surprisingly, the Hubble images taken March 16 with the new Advanced Camera for Surveys only show the single object Sedna, along with a faint, very distant background star in the same field of view.

“Despite HST’s crisp view (equivalent to trying to see a soccer ball 900 miles away), it still cannot resolve the disk of mysterious Sedna,” says Brown. This would place an upper limit in the object’s size of being approximately three-quarters the diameter of Pluto, or about 1,000 miles across.

But Brown predicted that a satellite would pop up as a companion “dot” in Hubble’s precise view. The object is not there, though there is a very small chance it might have been behind Sedna or transiting in front of it, so that it could not be seen separately from Sedna itself in the Hubble images.

Brown based this prediction on his earlier observations of apparent periodic changes in light reflecting from Sedna’s mottled surface. The resulting light curve gives a long rotation period exceeding 20 days (but not greater than 50 days). If true, Sedna would be the slowest rotating object in the solar system after Mercury and Venus, whose slow rotation rates are due to the tidal influence of the Sun.

One easy way out of this dilemma is the possibility that the rotation period is not as slow as the astronomers thought. But even with a careful reanalysis the team remains convinced that the period is correct. Brown admits, “I’m completely lost for an explanation as to why the object rotates so slowly.”

Small bodies like asteroids and comets typically complete one rotation in a matter of hours. Pluto’s rotation has been slowed to a relatively leisurely six-day period because Pluto is tidally locked to the revolution period of its satellite Charon. Hubble easily resolves Pluto and Charon as two separate bodies. NASA’s forthcoming James Webb Space Telescope will provide a platform for further high-resolution studies of the infrared light from such distant, cold bodies in our solar system.

The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).

Don Savage
NASA Headquarters, Washington
(Phone: 202-358-1547;

Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone: 410-338-4514;

Robert Tindol
California Institute of Technology, Pasadena, CA
(Phone: 626-395-3631;

Janet Emanuel
Yale University Office of Public Affairs, New Haven, CT
(Phone: 203-432-2157; E-mail:

HubbleSite – NewsCenter – Hubble Observes Planetoid Sedna, Mystery Deepens (04/14/2004) – Release Text.

Asteroid Will Pass Closer To Earth Than Many Satellites

Press Release
March 15, 2012

Mat Kaplan
Voice: 626-793-5100

In less than a year, an asteroid that is half the size of a football field will pass within just a few thousand miles of our planet. The discovery of this object, dubbed 2012 DA14, was made possible by a Shoemaker Near Earth Object (NEO) grant provided by the Planetary Society.

The giant space rock was discovered on February 22, 2012 by La Sagra Observatory in southern Spain. One of the observatory’s telescopes had recently been upgraded through the Planetary Society grant. Its new camera enabled detection of fast moving objects like 2012 DA14 – requiring very fast imaging for discovery and determination of their paths. The upgraded instrument has far outperformed the Observatory’s other telescopes. It has found more than ten NEOs, along with a previously unknown comet.

At fifty meters across, 2012 DA14 is similar in size to the object that caused the Tunguska air burst over Siberia in 1908, leveling 2,000 square kilometers of forest. Fortunately, there is no danger of impact during the next pass of 2012 DA14.

“This asteroid is a wakeup call for the importance of defending the Earth from future asteroid impacts,” says Bill Nye, Chief Executive Officer of The Planetary Society. “Big impacts don’t happen often, but they will happen.”

2012 DA14 will come closest to Earth on February 15, 2013. It will zoom to within about 3.5 Earth radii or about 22,500 km from the Earth’s surface, well within the orbit of geostationary communications satellites (35,800 km). Current estimates are that it will be about magnitude 7 in brightness – not quite visible to the naked eye, but within reach of binoculars or a small telescope. It will fly across the sky at about one Moon diameter per minute.

Additional follow-up by observers around the world has resulted in this accurate prediction of the asteroid’s current orbit by scientists at the Jet Propulsion Laboratory’s Near Earth Object Program Office. Knowing the close approach is coming will allow astronomers to study the characteristics of the asteroid. A major goal will be greater refinement of its orbit so that future close approaches and even possible impacts can be predicted and prepared for.

Jaime Nomen and his colleagues at La Sagra Observatory have introduced observing strategies designed to improve the probability of discovering asteroids that larger surveys may miss. Nomen reports, “We try to find smaller objects located close to Earth that generally move at high angular speed. They may appear anywhere in the sky, even if that sky region had already been thoroughly searched just days before.”

The strategy paid off. With the new CCD telescope camera configured to shoot rapid, short exposures, Nomen and his colleagues captured 2012 DA14 as it moved across the sky at almost 11 arcseconds per minute. This is slower than a satellite but quite fast for a NEO. It’s equivalent to a lunar diameter every three hours. The asteroid was already heading away from Earth after passing the planet about a week before, and at much greater distance than next year’s encounter. Its path across the eastern sky, fast angular motion, quite faint (and fading) brightness, and high declination (far above the ecliptic plane in which most of the planets travel) could easily have allowed 2012 DA14 to escape undetected.

Planetary Society Gene Shoemaker grants are awarded to amateur observers, observers in developing countries, and professional astronomers who, with seed funding, can greatly increase their programs’ contributions to NEO research. The program, begun in 1997, is named for Gene Shoemaker, a highly respected leader in the study of impact structures, and an advocate for NEO discovery and tracking programs.

The Planetary Society supports several projects that are helping to find near Earth objects and test techniques that may allow humanity to deflect a NEO that is headed toward a potentially catastrophic impact. The Society is committed to planetary defense. “Discovery, follow-up, and characterization of asteroids enabled by our Shoemaker grants is one of our most gratifying rewards,” says Bruce Betts, the organization’s Director of Projects. “We want to help humanity avoid the world’s only preventable natural disaster. Astronomers like those at La Sagra Observatory are critical to that goal. Their discovery and next year’s close approach will result in a scientific and planetary defense treasure trove of data.”

The 2012 DA14 flyby in 2013 will also serve as a warm-up for a similar fly by in 2029 by the much larger Apophis, a 270-meter asteroid co-discovered by Shoemaker NEO grant winner Roy Tucker.

For more information, including an update on the discovery and follow-up from Jaime Nomen of La Sagra Observatory, visit

About the Planetary Society
The Planetary Society has inspired millions of people to explore other worlds and seek other life. Today, its international membership makes the non-governmental Planetary Society the largest space interest group in the world. Carl Sagan, Bruce Murray and Louis Friedman founded the Planetary Society in 1980. Bill Nye, a long time member of the Planetary Society’s Board, is now the CEO.

Planetary Society
85 South Grand
Pasadena, CA 91105 USA
Voice: (626) 793-5100
Fax: (626) 793-5528

Draconid Meteor Shower on October 8, 2011 [May Damage International Space Station]

Sep 28, 2011; 6:36 AM ET

My astronomy expert, Daniel Vogler (well, Mark Comebellack is just as much of an expert), wrote on the AccuWeather astronomy facebook page, "Mark your calendar for October 8th. Draconid meteor shower time! Dust from the comet 21P/Giacobini-Zinner will give us falling star watchers a decent show, even though the full moon is four days later. One issue with this shower is that it may impact the ISS and possibly damage it. As far as viewing the actual peak times, it is in the daytime for U.S :(. 1 -2 PM EST. But check after sunset and you may get lucky. Europe has the best viewing for this one."

This meteor shower will be concentrated in the northwest sky. It will last for about 8 hours and be best seen just after sunset in the United States, if at all, as up to 1,000 meteors per hour will streak through Earth’s atmosphere, according to a recent study. Unfortunately, the flurry will peak around 1 p.m. or 2 p.m. EDT so by the time it is dark most, if not all, of the show will be done.

Like other meteor showers, the Draconids result when Earth plows through bits of debris shed by a comet on its path around the sun. In the Draconid’s case, this comet is called Giacobini-Zinner (hence the Draconid’s other name, the Giacobinids).

via – Astronomy | Draconid Meteor Shower.