Dawn bears down on Ceres

Ceres' cratered surface

More cool images! As Dawn moves in on Ceres and prepares to enter orbit on March 6, it has managed to assemble enough images to produce a global map of the almost spheroid-shaped giant asteroid.

The bright spots however remain a mystery which cannot be answered until we get higher resolution images from much closer. Hopefully, Dawn will be able to do this once it is in orbit.

The brightest spot on Ceres has a partner

Ceres' double bright spots

Cool images! Dawn’s newest images have revealed that the brightest spot on Ceres, shown on the right in a cropped version of the full image, has a dimmer companion.

“Ceres’ bright spot can now be seen to have a companion of lesser brightness, but apparently in the same basin. This may be pointing to a volcano-like origin of the spots, but we will have to wait for better resolution before we can make such geologic interpretations,” said Chris Russell, principal investigator for the Dawn mission, based at the University of California, Los Angeles.

The spots are still too small for Dawn’s camera to resolve. That they are inside what looks like a crater is very puzzling. If they are water-ice, why are they so bright and distinct? One one think the ice would pile up along the crater wall, but then, that’s what we think based on our experience here on Earth with wind, rain, and our heavy gravity. Ceres is cold, has no atmosphere, and a tiny gravitational field. Every geological process will proceed in a different manner.

Ceres comes into focus

Ceres as since on February 12, 2015 by Dawn

Cool images! The Dawn science team has released new even sharper images of the giant asteroid Ceres, taken by Dawn on February 12 at a distance of 52,000 miles.

Though the surface appears to have many of the typical craters, scientists continue to be puzzled by the bright spots. This newest image suggests that they are ice-filled craters, but don’t hold me to that guess. For one thing, why are only a handful of craters filled with ice, and none of the others?

Dawn’s arrival at Ceres delayed one month

Though engineers have solved the problems caused when a radiation blast disabled Dawn’s ion engine and put it into safe mode for a week, the fix will cause a one month delay in its arrival at the asteroid Ceres.

Controllers discovered Dawn was in safe mode Sept. 11 after radiation disabled its ion engine, which uses electrical fields to “push” the spacecraft along. The radiation stopped all engine thrusting activities. The thrusting resumed Monday (Sept. 15) after controllers identified and fixed the problem, but then they found another anomaly troubling the spacecraft.

Dawn’s main antenna was also disabled, forcing the spacecraft to send signals to Earth (a 53-minute roundtrip by light speed) through a weaker secondary antenna and slowing communications. The cause of this problem hasn’t been figured out yet, but controllers suspect radiation affected the computer’s software. A computer reset has solved the issue, NASA added. The spacecraft is now functioning normally.

Astronomers have detected water vapor spurting from Ceres, the solar system’s largest asteroid.

Using the Herschel Space Telescope astronomers have detected water vapor spurting from Ceres, the solar system’s largest asteroid.

Herschel’s sensors spied plumes during three of the four observation periods. The strength of absorption varied over a matter of hours, a trend probably caused by relatively small sources of water vapour rotating in and out of view of Earth, the researchers say.

Data gathered in March 2013 suggest that the plumes originated from two widely separated, 60-kilometre-wide spots in the dwarf planet’s mid-latitude regions. Together, these spots ejected about 6 kilograms of water vapour into space each second. Neither ground-based observations nor images from the Hubble Space Telescope are keen enough to identify the as-yet-mysterious areas, says Küppers. “We don’t know what these features are, we just know that they’re darker than their surroundings,” he notes.

The NASA probe Dawn will arrive at Ceres early next year, and take a good look at these plumes. Should be exciting.

An update on Dawn in its journey from the asteroids Vesta to Ceres.

An update on Dawn in its journey from the asteroids Vesta to Ceres. Bottom line:

Dawn is 18 million kilometers (11 million miles) from Vesta and 50 million kilometers (31 million miles) from Ceres. It is also 3.47 AU (519 million kilometers or 322 million miles) from Earth, or 1,310 times as far as the moon and 3.42 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 58 minutes to make the round trip.

One of Dawn’s reaction wheels, used to orient the spacecraft, shut down last week.

Uh-oh: One of Dawn’s reaction wheels, used to orient the spacecraft, shut down last week.

During a planned communications pass on Aug. 9, the team learned that the reaction wheel had been powered off. Telemetry data from the spacecraft suggest the wheel developed excessive friction, similar to the experience with another Dawn reaction wheel in June 2010. The Dawn team demonstrated during the cruise to Vesta in 2011 that, if necessary, they could complete the cruise to Ceres without the use of reaction wheels.

That the spacecraft can get to Ceres without reaction wheels is good. However, can it be oriented precisely to do science without these wheels? The JPL press release does not say.

Dawn has begun its slow departure from Vesta in anticipation of its journey to the solar system’s largest asteroid, Ceres.

Dawn has begun its slow departure from Vesta in anticipation of its journey to the solar system’s largest asteroid, Ceres.

The departure was actually announced two weeks ago, but since this is a very slow process it isn’t like we have missed anything. Dawn’s ion engines are very efficient, but they work at a very leisurely pace. It will take a month for the engine’s thrusters to push Dawn out of its orbit around Vesta.

Bad news for climate modelers

A new analysis of the orbits of Ceres and Vesta says that in a surprisingly short time those orbits become chaotic and therefore unpredictable. More significantly, those orbits interact with the Earth’s and also make its long term orbit chaotic and unpredictable. From the abstract:

Although small, Ceres and Vesta gravitationally interact together and with the other planets of the Solar System. Because of these interactions, they are continuously pulled or pushed slightly out of their initial orbit. Calculations show that, after some time, these effects do not average out. Consequently, the bodies leave their initial orbits and, more importantly, their orbits are chaotic, meaning that we cannot predict their positions. The two bodies also have a significant probability of impacting each other, estimated at 0.2% per billion year. Last but not least, Ceres and Vesta gravitationally interact with the Earth, whose orbit also becomes unpredictable after only 60 million years. This means that the Earth’s eccentricity, which affects the large climatic variations on its surface, cannot be traced back more than 60 million years ago. This is indeed bad news for Paleoclimate studies. [emphasis mine]

The scientists found that it became impossible to calculate the orbits of the two largest asteroids after only several ten thousand years. They also found that “numerous asteroids in the main belt will behave in the same way with . . . much more chaotic behavior than previously thought.” Worse, the possibility of collisions was far higher than ever thought. Ceres and Vesta have a 1 in 500 chance of colliding with each other every billion years, while other asteroids have chances as low as 1 in 1000.

The importance of this discovery, which still needs to be confirmed by other researchers, cannot be understated.
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