Category Archives: Comets

Comet Hunter – Shoemaker(s) and Levi

SOHO maybe the most successful space based comet hunters but it is very difficult to talk about the best comet hunters without including Eugene and Carolyn Shoemaker and David Levy. They have many comet discoveries to their credit including the famous Shoemaker-Levi 9 comet.

Video

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.

Comet Dust

Dust particles from Comet 67P/Churyumov-Gerasimenko collected by ESA's Rosetta spacecraft. Copyright ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/ BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S
Dust particles from Comet 67P/Churyumov-Gerasimenko collected by ESA’s Rosetta spacecraft. Copyright ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/ BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S

One of the instruments on board ESA’s Rosetta called COSIMA, short for the COmetary Secondary Ion Mass Analyser one of three dust analysis experiments.

Essentially this instrument has a plate for catching dust grains from the comet at fairly low speeds. The dust grains shown above is two of the grains collected and they have yielded some interesting results.

I’ll let ESA explain:

Two examples of dust grains collected by Rosetta’s COmetary Secondary Ion Mass Analyser (COSIMA) instrument in the period 25–31 October 2014. Both grains were collected at a distance of 10–20 km from the comet nucleus. Image (a) shows a dust particle (named by the COSIMA team as Eloi) that crumbled into a rubble pile when collected; (b) shows a dust particle that shattered (named Arvid).

For both grains, the image is shown twice under two different grazing illumination conditions: the top image is illuminated from the right, the bottom image from the left. The brightness is adjusted to emphasise the shadows, in order to determine the height of the dust grain. Eloi therefore reaches about 0.1 mm above the target plate; Arvid about 0.06 mm. The two small grains at the far right of image (b) are not part of the shattered cluster.

The fact that the grains broke apart so easily means their individual parts are not well glued together. If they contained ice they would not shatter; instead, the icy component would evaporate off the grain shortly after touching the collecting plate, leaving voids in what remained. By comparison, if a pure water-ice grain had struck the detector, then only a dark patch would have been seen.

These ‘fluffy’ grains are thought to originate from the dusty layer built up on the comet’s surface since its last close approach to the Sun, and will soon be lost into the coma.

Be sure to check the Rosetta Blog. The have this and results from six other Rosetta’s science instruments since arriving at Comet 67P/Churyumov-Gerasimenko – great stuff!!

Cometary Wisps

Rosetta images the dust coming off Comet 67P/Churyumov-Gerasimenko  Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Rosetta images the dust coming off Comet 67P/Churyumov-Gerasimenko Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

ESA’s Rosetta spacecraft took this image of Comet 67P/Churyumov-Gerasimenko last November with the OSIRIS camera. By overexposing the comet the wisps of cometary dust is highlighted.

Rosetta has an instrument called MIDAS and its job is to capture 67P/C-G particles. About the time this image was taken MIDAS captured a particle measuring 10 micrometres, which is way larger than was expected.

From the Rosetta blog (be sure to check it out)

“This is still the beginning of the activity compared to what we expect to see in summer this year,” says OSIRIS principal investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. “From the last perihelion passage we know that the comet will evolve by a factor of 100 in activity at that time compared to now.”

See Comet Lovejoy Tonight

A beautiful image of Comet Lovejoy from Andrew Dumont.
A beautiful image of Comet Lovejoy from Andrew Dumont.

Want to see a comet?

You can see this comet for yourself. The comet C/2014 Q2 or Comet Lovejoy is easily visible with binoculars. If you can see the constellation Orion and Taurus you should be all set.

I just used the finders chart from NASA (see it here). Stepped out on back porch and after watching a satellite pass over, found the Comet in just a couple of minutes. I did use binoculars (could not see the comet otherwise). The binoculars were nothing special so if you have a pair handy give it a try. If you have a even a small telescope this looks really cool.

Cloudy skies?  The comet will be around for a bit so don’t worry if you have to wait a short time.

Could it be visible with the naked eye?  I would think so.  I am going to try in the morning, the best skies I get.  I could not see it a while ago, too cold to be outside for too long and not be well prepared, so I can’t say for sure.