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).

CONTACT
Don Savage
NASA Headquarters, Washington
(Phone: 202-358-1547; dsavage@hq.nasa.gov)

Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone: 410-338-4514; villard@stsci.edu)

Robert Tindol
California Institute of Technology, Pasadena, CA
(Phone: 626-395-3631; tindol@caltech.edu)

Janet Emanuel
Yale University Office of Public Affairs, New Haven, CT
(Phone: 203-432-2157; E-mail: janet.emanuel@yale.edu)

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

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It’s called Apophis. It’s 390m wide. And it could hit Earth in 24 years’ time.

Scientists call for plans to change asteroid’s path.
Developing technology could take decades.

Alok Jha
The Guardian, Tuesday 6 December 2005

In Egyptian myth, Apophis was the ancient spirit of evil and destruction, a demon that was determined to plunge the world into eternal darkness.

A fitting name, astronomers reasoned, for a menace now hurtling towards Earth from outerspace. Scientists are monitoring the progress of a 390-metre wide asteroid discovered last year that is potentially on a collision course with the planet, and are imploring governments to decide on a strategy for dealing with it.

Nasa has estimated that an impact from Apophis, which has an outside chance of hitting the Earth in 2036, would release more than 100,000 times the energy released in the nuclear blast over Hiroshima. Thousands of square kilometres would be directly affected by the blast but the whole of the Earth would see the effects of the dust released into the atmosphere.

And, scientists insist, there is actually very little time left to decide. At a recent meeting of experts in near-Earth objects (NEOs) in London, scientists said it could take decades to design, test and build the required technology to deflect the asteroid. Monica Grady, an expert in meteorites at the Open University, said: “It’s a question of when, not if, a near Earth object collides with Earth. Many of the smaller objects break up when they reach the Earth’s atmosphere and have no impact. However, a NEO larger than 1km [wide] will collide with Earth every few hundred thousand years and a NEO larger than 6km, which could cause mass extinction, will collide with Earth every hundred million years. We are overdue for a big one.”

Apophis had been intermittently tracked since its discovery in June last year but, in December, it started causing serious concern. Projecting the orbit of the asteroid into the future, astronomers had calculated that the odds of it hitting the Earth in 2029 were alarming. As more observations came in, the odds got higher.

Having more than 20 years warning of potential impact might seem plenty of time. But, at last week’s meeting, Andrea Carusi, president of the Spaceguard Foundation, said that the time for governments to make decisions on what to do was now, to give scientists time to prepare mitigation missions. At the peak of concern, Apophis asteroid was placed at four out of 10 on the Torino scale – a measure of the threat posed by an NEO where 10 is a certain collision which could cause a global catastrophe. This was the highest of any asteroid in recorded history and it had a 1 in 37 chance of hitting the Earth. The threat of a collision in 2029 was eventually ruled out at the end of last year.

Alan Fitzsimmons, an astronomer from Queen’s University Belfast, said: “When it does pass close to us on April 13 2029, the Earth will deflect it and change its orbit. There’s a small possibility that if it passes through a particular point in space, the so-called keyhole, … the Earth’s gravity will change things so that when it comes back around again in 2036, it will collide with us.” The chance of Apophis passing through the keyhole, a 600-metre patch of space, is 1 in 5,500 based on current information.

There are no shortage of ideas on how to deflect asteroids. The Advanced Concepts Team at the European Space Agency have led the effort in designing a range of satellites and rockets to nudge asteroids on a collision course for Earth into a different orbit.

No technology has been left unconsidered, even potentially dangerous ideas such as nuclear powered spacecraft. “The advantage of nuclear propulsion is a lot of power,” said Prof Fitzsimmons. “The negative thing is that … we haven’t done it yet. Whereas with solar electric propulsion, there are several spacecraft now that do use this technology so we’re fairly confident it would work.”

The favoured method is also potentially the easiest – throwing a spacecraft at an asteroid to change its direction. Esa plans to test this idea with its Don Quixote mission, where two satellites will be sent to an asteroid. One of them, Hidalgo, will collide with the asteroid at high speed while the other, Sancho, will measure the change in the object’s orbit. Decisions on the actual design of these probes will be made in the coming months, with launch expected some time in the next decade. One idea that seems to have no support from astronomers is the use of explosives.

Prof Fitzsimmons. “If you explode too close to impact, perhaps you’ll get hit by several fragments rather than one, so you spread out the area of damage.”

In September, scientists at Strathclyde and Glasgow universities began computer simulations to work out the feasibility of changing the directions of asteroids on a collision course for Earth. In spring next year, there will be another opportunity for radar observations of Apophis that will help astronomers work out possible future orbits of the asteroid more accurately.

If, at that stage, they cannot rule out an impact with Earth in 2036, the next chance to make better observations will not be until 2013. Nasa has argued that a final decision on what to do about Apophis will have to be made at that stage.

“It may be a decision in 2013 whether or not to go ahead with a full-blown mitigation mission, but we need to start planning it before 2013,” said Prof Fitzsimmons. In 2029, astronomers will know for sure if Apophis will pose a threat in 2036. If the worst-case scenarios turn out to be true and the Earth is not prepared, it will be too late. “If we wait until 2029, it would seem unlikely that you’d be able to do anything about 2036,” said Mr Yates.

It’s called Apophis. It’s 390m wide. And it could hit Earth in 31 years’ time | Science | The Guardian.

Hubble Telescope Spots Complex Organic Molecules On Surface Of Pluto

Published December 21, 2011 | Space.com

NASA, ESA, and M. Buie (Southwest Research Institute)
Dwarf planet Pluto is seen in an image taken by the Hubble Space Telescope.

The Hubble Space Telescope has spotted new evidence of complex organic molecules — the carbon-containing building blocks of life as we know it — on the frigid surface of Pluto, a new study finds.

Hubble observations revealed that some substances on Pluto’s surface are absorbing more ultraviolet light than expected. The compounds in question may well be organics, possibly complex hydrocarbons or nitrogen-containing molecules, researchers said.

The dwarf planet Pluto is known to harbor ices of methane, carbon monoxide and nitrogen on its surface. The ultraviolet-absorbing chemical species may have been produced when sunlight or super-speedy subatomic particles known as cosmic rays interacted with these ices, researchers said.

“This is an exciting finding because complex Plutonian hydrocarbons and other molecules that could be responsible for the ultraviolet spectral features we found with Hubble may, among other things, be responsible for giving Pluto its ruddy color,” study leader Alan Stern, of the Southwest Research Institute in Boulder, Colo., said in a statement.

Pluto circles the sun in a distant ring of icy bodies known as the Kuiper Belt. Many other Kuiper Belt objects are also quite red, and researchers have previously speculated that organics are responsible for their ruddiness as well.

Stern and his colleagues also found that Pluto’s ultraviolet spectrum has changed compared to Hubble measurements taken during the 1990s. They used Hubble’s powerful Cosmic Origins Spectrograph instrument to make the find.

These differences may be related to changes in the dwarf planet’s terrain since then, researchers said. It’s possible that a steep increase in Pluto’s atmospheric pressure has caused changes in Pluto’s surface, they added.

Overall, the new Hubble observations shed further light on Pluto a few years ahead of the first-ever spacecraft visit to the cold, distant world.

“The discovery we made with Hubble reminds us that even more exciting discoveries about Pluto’s composition and surface evolution are likely to be in store when NASA’s New Horizons spacecraft arrives at Pluto in 2015,” Stern said.

New Horizons launched in January 2006 on a 4-billion-mile (6.4-billion-kilometer) journey to Pluto. The probe is due to make its closest approach to the dwarf planet on July 14, 2015. On that date, New Horizons will be just 7,767 miles (12,500 km) away from the frigid world.

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