All posts by Tom

Iapetus

The Saturn moon Iapetus from Cassini
The Saturn moon Iapetus from Cassini

Here’s an image of the Saturn moon Iapetus from the Cassini spacecraft. It is the third largest moon of Saturn with a diameter of 1,417 km / 914 miles or about 40 percent of our moon . Iapetus has density of 1.1 so we know it is made largely of ices.

It’s a strange moon. Take note of the dark spot, that’s not a shadow. Iapetus has a dark side to it that has nothing to do whether or not it is facing the Sun. What causes the asymmetry? There are a few theories, the latest (and my new favorite) is due to ice migration in what is known as the Thermal Runaway Model.

Check out our Iapetus page for more images and more about the moon including physical details.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

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Dawn in Orbit

Dawn in orbit. Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Dawn in orbit. Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

NASA’s Dawn spacecraft entered an orbit around the dwarf planet Ceres.

The spacecraft was captured by the gravitational pull of Ceres at 07:39 EST / 12:39 UTC on 06 March 2015.

The confirmation came when JPL recieved a signal from Dawn that it was healthy and the ion engine was thrusting as expected.

The image above from the spacecraft was taken about the time of orbital entry at a distance of 61,000 / 38,000 miles from Ceres. I believe this will be one of the last images we will see for a short while as Dawn is on the side of Ceres away from the sun so it is too dark for imaging. The spacecraft will return to the lit side in April.

More at NASA

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The Old Ocean on Mars

All the clues lead to the idea there was water on Mars, little dispute there. How much water there was is the question. Scientists at Goddard Space Flight Center (NASA) suggest the planet was 20 percent covered with water.

The following question has to be:  was the water there long enough for life to exist?

Video

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Speeding Star

An artist impression of the mass-transfer phase followed by a double-detonation supernova that leads to the ejection of US 708.  CREDIT: ESA/HUBBLE, NASA, S. GEIER
An artist impression of the mass-transfer phase followed by a double-detonation supernova that leads to the ejection of US 708. CREDIT: ESA/HUBBLE, NASA, S. GEIER

Scientists using the W.M. Keck Observatory and Pan-STARRS1 telescopes have discovered a star that breaks a speed record. This star is traveling at 1,200 km/sec (2.7 million miles per hour). Fast enough so the star will escape the gravity of the galaxy and leave. Only a handful of such stars are known.

This star was part of a binary star system and was ejected by a supernova explosion. The image above is an artist impression and it shows the star to the left and the supernova at the same time but the supernova would have faded away by the time the star hit that position.

The hypervelocity stars are destined to spend their lives speeding through intergalactic space although it is thought usually such stars get ejected due to a close encounter with the black hole at the center of Milky Way.

While the image shown here is an artist concept, scientists observed this star called US 708 with the Echellette Spectrograph and Imager instrument on the 10-meter, Keck II telescope to measure its distance and velocity along our line of sight. By combining position measurements from the archives with new measurements from Pan-STARRS1, scientists were able to come up with the star’s velocity across our line of sight. The trajectory of the star shows the velocity cannot be from an encounter with a black hole.

There’s more (from the Keck press release):

US 708 has another peculiar property in marked contrast to other hypervelocity stars: it is a rapidly rotating, compact helium star likely formed by interaction with a close companion. Thus, US 708 could have originally resided in an ultra compact binary system, transferring helium to a massive white dwarf companion, ultimately triggering a thermonuclear explosion of a type Ia supernova. In this scenario, the surviving companion, i.e. US 708, was violently ejected from the disrupted binary as a result, and is now traveling with extreme velocity.

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Problem with Curiosity

A picture of the drilling section of Curiosity from the rover's MAST cam.  This is a raw image directly from the camera and not white balanced. Image Credit: NASA/JPL-Caltech/MSSS
A picture of the drilling section of Curiosity from the rover’s MAST cam. This is a raw image directly from the camera and not white balanced. Image Credit: NASA/JPL-Caltech/MSSS

A problem has developed with the Mars Science Laboratory also known as Curiosity.

The image above shows the drill section of the rover after it finished drilling into “Telegraph Peak” on 24 February 2015. On 27 February 2015 as the sample was being transferred the sample powder obtained from the drilling process an electrical “irregularity” triggered a fault-protection event. The fault-protection event halted the process because it stopped the arm activity.

Telemetry indicates a transient short circuit occurred prompting the pre-programmed response to the anomolous condition by stopping activity; hopefully sparing the rover further damage. Mission managers are running tests and will continue to work through the problem. In all likelyhood Curiosity will be back to work soon — stay tuned.

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Rosetta’s Shadow

Rosetta's shadow on Comet 67/C-G taken on 14 February 2015. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Rosetta’s shadow on Comet 67/C-G taken on 14 February 2015. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Here’s something you don’t see very often or ever for that matter. We can see the shadow of ESA’s Rosetta spacecraft on Comet 67P/Churyumov-Gerasimenko.

During the close flybys of a couple week ago, only 6 km separated spacecraft and comet. During the flyby the sun was directly between sun and comet so a shadow of about 20 x 50 meters (66 x 164 feet) was projected onto the comet. ESA was able to capture the image with the OSIRIS camera.

The pair were about 2.35 AU from the Sun so if I did the math correctly the light levels would be approximately 5.5 times less bright than what we see around us.

Approximate brightness relative to us is about the distance in AU (astronomical units) to the power of 2,

2.35 AU 2 = 5.5 (in this case 5.5 X dimmer)

Is this a first? I can’t think of any example of shadows on other comet encounters.

ESA has a nice write up and more pictures at the Rosetta blog, check it out.

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Dawn Almost Home

ceresfeb25
Click for a larger version.

The Dawn spacecraft is just days away from entering an orbit around the dwarf planet Ceres. The pictures are becoming better and more detailed raising anticipation for what we might learn. For starters, what makes the mystery bright spots bright and how was that “pancake” feature / crater formed? You can see the latter on the right hand image on the lower horizon and a nice view of it here (taken on 19 February 2015).

This image was taken on 25 February 2015 from a distance of 40,000 km / 25,000 miles.

Dawn website

Image(s) Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

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Hubble’s View of NGC 4424

Hubble's image of NGC 4424 in the Virgo Cluster. Copyright ESA/Hubble & NASA
Hubble’s image of NGC 4424 in the Virgo Cluster. Copyright ESA/Hubble & NASA

The Virgo Cluster of galaxies, home to NGC 4424 is about 15.6 million parsecs (54 million light-years) away.

ESA’s caption:

The galaxy pictured here is NGC 4424, located in the constellation of Virgo. It is not visible with the naked eye but has been captured here with the NASA/ESA Hubble Space Telescope.

Although it may not be obvious from this image, NGC 4424 is in fact a spiral galaxy. In this image it is seen more or less edge on, but from above you would be able to see the arms of the galaxy wrapping around its centre to give the characteristic spiral form .

In 2012 astronomers observed a supernova in NGC 4424 — a violent explosion marking the end of a star’s life. During a supernova explosion, a single star can often outshine an entire galaxy. However, the supernova in NGC 4424, dubbed SN 2012cg, cannot be seen here as the image was taken ten years prior to the explosion. Along the central region of the galaxy, clouds of dust block the light from distant stars and create dark patches.

To the left of NGC 4424 there are two bright objects in the frame. The brightest is another, smaller galaxy known as LEDA 213994 and the object closer to NGC 4424 is an anonymous star in our Milky Way.

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