Category Archives: Comets

Moving a Boulder on a Comet

Take a look at these images of a boulder that moved on Comet 67P/Churyumov-Gerasimenko as seen by the Rosetta spacecraft.  Fascinating stuff.  The boulder clearly moved.  But how?

Here’s ESA’s caption (via NASA):
A 100 foot-wide (30 meter), 28-million-pound (12.8-million-kilogram) boulder, was found to have moved 460 feet (140 meters) on comet 67P/Churyumov-Gerasimenko in the lead up to perihelion in August 2015, when the comet’s activity was at its highest. In both images, an arrow points to the boulder; in the right-hand image, the dotted circle outlines the original location of the boulder for reference.

The movement could have been triggered in one of two ways: either the material on which it was sitting eroded away, allowing it to roll downslope, or a sufficiently forceful outburst could have directly lifted it to the new location. Indeed, several outburst events were detected close to the original position of the boulder during perihelion.

The images were taken by Rosetta’s OSIRIS camera on May 2, 2015 (left) and Feb. 7, 2016 (right), with resolutions of 7.5 feet (2.3 meters) per pixel and 2.6 feet (0.8 meters) per pixel, respectively.

Rosetta is a European Space Agency mission with contributions from its member states and NASA. Rosetta’s Philae lander is provided by a consortium led by the German Aerospace Center, Cologne; Max Planck Institute for Solar System Research, Gottingen; French National Space Agency, Paris; and the Italian Space Agency, Rome. NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the U.S. participation in the Rosetta mission for NASA’s Science Mission Directorate in Washington.

So first I’m siding with the erosion idea by way of off gassing or jets. It seems that a jet strong enough to directly lift a “12.8 million-kg” boulder would lift more material than just the boulder and if it did the boulder would likely show more of an impact mark as the soil looks sand-like. True the same forces could erase those marks but you’d think there would be some physical sign of such a powerful event. Still there are no “boulder-tracks” and again off-gassing might erase the tracks.

The other thing that isn’t explained is this: Is the 12.8 million-kg / 28 million-lb boulder a true 67P weight or is that what it would weigh here on Earth?  OR is this a measure of mass but not stated as such? This is a case where knowing the mass would be helpful. Like I said – fascinating stuff!



The comet 45P/Honda-Mrkos-Pajdusakova makes a close approach to us here on Earth as it will this time around.  The distance between us is just 0.083 A.U or 12.4 million km or 7.7 million miles at close approach.  You’d think we could see it but no because the Sun is so much brighter.

45P/Honda can be seen before daylight in the eastern sky, but you will need a telescope or a good pair of binoculars and a nice dark sky.

The image above was taken on 09 January 2017 by Jean-Francois Soulier.

See the full image here.

Here Comes Another Comet

Hot on the heels of 45P/Honda, here comes C/2016 U1 NEOWISE and it might be visible with binoculars by next week – maybe.  2016 U1 NEOWISE is a telescope target right now and even a modest telescope should see it.

But wait, there’s more!  We may have another possible comet called 2016 WF9 coming too; “possible” being the key-word because we just don’t know for sure.


Here’s the story from NASA:
NASA’s NEOWISE mission has recently discovered some celestial objects traveling through our neighborhood, including one on the blurry line between asteroid and comet. Another–definitely a comet–might be seen with binoculars through next week.

An object called 2016 WF9 was detected by the NEOWISE project on Nov. 27, 2016. It’s in an orbit that takes it on a scenic tour of our solar system. At its farthest distance from the sun, it approaches Jupiter’s orbit. Over the course of 4.9 Earth-years, it travels inward, passing under the main asteroid belt and the orbit of Mars until it swings just inside Earth’s own orbit. After that, it heads back toward the outer solar system. Objects in these types of orbits have multiple possible origins; it might once have been a comet, or it could have strayed from a population of dark objects in the main asteroid belt.

2016 WF9 will approach Earth’s orbit on Feb. 25, 2017. At a distance of nearly 32 million miles (51 million kilometers) from Earth, this pass will not bring it particularly close. The trajectory of 2016 WF9 is well understood, and the object is not a threat to Earth for the foreseeable future.

A different object, discovered by NEOWISE a month earlier, is more clearly a comet, releasing dust as it nears the sun. This comet, C/2016 U1 NEOWISE, “has a good chance of becoming visible through a good pair of binoculars, although we can’t be sure because a comet’s brightness is notoriously unpredictable,” said Paul Chodas, manager of NASA’s Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California.

As seen from the northern hemisphere during the first week of 2017, comet C/2016 U1 NEOWISE will be in the southeastern sky shortly before dawn. It is moving farther south each day and it will reach its closest point to the sun, inside the orbit of Mercury, on Jan. 14, before heading back out to the outer reaches of the solar system for an orbit lasting thousands of years. While it will be visible to skywatchers at Earth, it is not considered a threat to our planet either.

NEOWISE is the asteroid-and-comet-hunting portion of the Wide-Field Infrared Survey Explorer (WISE) mission. After discovering more than 34,000 asteroids during its original mission, NEOWISE was brought out of hibernation in December of 2013 to find and learn more about asteroids and comets that could pose an impact hazard to Earth. If 2016 WF9 turns out to be a comet, it would be the 10th discovered since reactivation. If it turns out to be an asteroid, it would be the 100th discovered since reactivation.

What NEOWISE scientists do know is that 2016 WF9 is relatively large: roughly 0.3 to 0.6 mile (0.5 to 1 kilometer) across.

It is also rather dark, reflecting only a few percent of the light that falls on its surface. This body resembles a comet in its reflectivity and orbit, but appears to lack the characteristic dust and gas cloud that defines a comet.

“2016 WF9 could have cometary origins,” said Deputy Principal Investigator James “Gerbs” Bauer at JPL. “This object illustrates that the boundary between asteroids and comets is a blurry one; perhaps over time this object has lost the majority of the volatiles that linger on or just under its surface.”

Near-Earth objects (NEOs) absorb most of the light that falls on them and re-emit that energy at infrared wavelengths. This enables NEOWISE’s infrared detectors to study both dark and light-colored NEOs with nearly equal clarity and sensitivity.

“These are quite dark objects,” said NEOWISE team member Joseph Masiero, “Think of new asphalt on streets; these objects would look like charcoal, or in some cases are even darker than that.”

NEOWISE data have been used to measure the size of each near-Earth object it observes. Thirty-one asteroids that NEOWISE has discovered pass within about 20 lunar distances from Earth’s orbit, and 19 are more than 460 feet (140 meters) in size but reflect less than 10 percent of the sunlight that falls on them.

Close Encounter with a Comet

Here we have radar pictures of comet P/2016 BA14. The images were taken with an antenna of NASA’s Deep Space Network at Goldstone, California on 23 March 2016 when the comet was only 3.6 million km / 2.2 million miles from Earth.

Astronomers at the Planetary Science Institute also observed the comet with the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. Very cool findings

Here is PSI’s press release:
March 24, 2016, Tucson, Ariz. — Astronomers at the Planetary Science Institute made observations of Comet Pan-STARRS (P/2016 BA14) using the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawai’i that show that it reflects less than 3 percent of the sunlight that falls on its surface. For comparison, fresh asphalt reflects about 4 percent of the light that falls on it.

Comet Pan-STARRS made a close flyby of the Earth at a distance of 3.6 million kilometers (2.2 million miles) on March 22. This is one of the closest flybys of a comet in recorded history and the last one to come closer was Lexell’s comet that flew by the Earth at a distance of 2.2 million kilometers (1.4 million miles) on July 1, 1770.

“We measured the spectral and thermal properties of the comet using the NASA IRTF and found that the comet reflects between 2-3 percent of the sunlight that falls on it,” said Vishnu Reddy, research scientist at the Planetary Science Institute in Tucson, Arizona. “This is typical for comets,” Reddy added. Based on its reflective properties, Reddy estimates the size of the comet to be between 600 meters and 1.2 kilometers (0.4 miles and 0.75 miles) in diameter.

Comet Pan-STARRS was originally discovered as an asteroid and later found to have cometary properties when astronomers realized its orbit is similar to another short period comet 252P/LINEAR, which also made a close flyby of the Earth at 5.3 million kilometers (3.3 miles) on March 21.

“It is an extremely rare opportunity to be able to study a pair of comets with historically close flybys. Measuring the physical properties of both comets will help us understand the evolution of comets in general,” said Jian-Yang Li, Senior Scientist at PSI. Li was observing 252P/LINEAR with the Hubble Space Telescope during its close encounter.

This research was funded by NASA Near-Earth Object Observations program. The Infrared Telescope Facility is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration.

Image: NASA/JPL-Caltech/GSSR

Comet Catalina


UPDATE: I was clouded in this morning so after looking at satellite image I drove about 16 km north and I found Catalina to be a naked-eye comet.  It is pretty small but if you have even a small pair of binoculars it is easy to see.

A beautiful shot of Comet Catalina in the northern sky the other morning.  This image was taken about 60 km east of here before sunrise.

Comet Catalina is a binocular object about now and is pretty easy to find in the morning sky.  Yes, should be worth getting up early for.   To find Catalina, locate the “Plough  or Big Dipper”  follow along the handle and look about half way between the last star in the “handle” (the star is named Alkaid) and the star Arcturus.

To make it a little easier, I’ve located the stars with red asterisks here.  Make sure you have binoculars and your eyes are dark adapted.  Go outside and stay out of any bright light sources for a few minutes (15 is good) and have a look.

Thanks for the awesome image Andrew!

Neowise and Comet Christensen



This is a great press release, I believe I saw this comet back in 2009 I need to look back and see if I did, I’m pretty sure though.

Christensen has a period of 2,409,303 years!

Other Christensen facts at Heavens Above.

The Newowise caption:

An infrared view from NASA’s NEOWISE mission of the Oort cloud comet C/2006 W3 (Christensen). The spacecraft observed this comet on April 20th, 2010 as it traveled through the constellation Sagittarius. Comet Christensen was nearly 370 million miles (600 million kilometers) from Earth at the time.

The image is half of a degree of the sky on each side. Infrared light with wavelengths of 3.4, 12 and 22 micron channels are mapped to blue, green, and red, respectively. The signal at these wavelengths is dominated primarily by the comet’s dust thermal emission, giving it a golden hue.

The WISE spacecraft was put into hibernation in 2011 upon completing its goal of surveying the entire sky in infrared light. WISE cataloged three quarters of a billion objects, including asteroids, stars and galaxies. In August 2013, NASA decided to reinstate the spacecraft on a mission to find and characterize more asteroids.

JPL manages NEOWISE for NASA’s Science Mission Directorate at the agency’s headquarters in Washington. The Space Dynamics Laboratory in Logan, Utah, built the science instrument. Ball Aerospace & Technologies Corp. of Boulder, Colorado, built the spacecraft. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

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.