Category Archives: Comets

Comet 21P Flies By

Edit: Flys? Flies is of course correct. Funny because I actually looked this up and STILL did it wrong – LOL.

What a very nice image of Comet 21 P//Giacobini-Zinner by Greg Ruppel (this image via ESA). Very nice indeed, it’s not as easy to do as one might think. Heh, I came to that conclusion about 2 seconds after I tried it. Fun though.

I wanted to mention we could have a naked-eye comet on the way. The comet is 46P/Wirtanen and could be down around a magnitude 3 in December and with decent skies it should be visible. Note that comets are not necessarily like stars in terms of brightness as comets are more diffuse. More on 46P/Wirtanen later.

As for comet 21P ESA included a great companion story: Something small and green recently flittered across our skies. On 10 September, comet 21P/Giacobini-Zinner made its closest approach to the Sun in 72 years — 151 million km from our star and just 58.6 million km away from Earth (about a third of the distance from here to the Sun).Discovered in 1900, this small comet reappears every 6.6 years. At just two km in diameter, 21P’s cometary tail contains a stream of ‘cometary crumbs’, and as Earth moves through this stream of debris it creates the Draconid meteor shower which peaks every year around 8 October.

Comets are leftovers of the formation of the Solar System, and while they are typically less dense than asteroids they pass Earth at relatively higher speeds, meaning the impact energy of a comet’s nucleus is slightly larger than that of a similar-sized asteroid.

Although no comet is conclusively known to have impacted Earth, there are many proponents of the theory that a fragment of Comet Encke — a periodic comet that orbits the Sun every 3.3 years — resulted in one of the most well-known impact events in our planet’s history.

In 1930, the British astronomer F.J.W. Whipple suggested that the Tunguska event of 1908 — in which an explosion over Eastern Siberia Taiga flattened 2000 square km of forest — was in fact the result of a cometary impact.

No impact crater was ever found, and glowing skies were reported across Europe for several evenings after the event, both supporting the notion that a comet, composed of dust and volatiles — such as water ice and frozen gases — could have been completely vaporised as it smashed into Earth’s atmosphere leaving no obvious trace.

In order to better understand the risk that asteroids and comets pose to our planet, we need to better understand their orbit and composition. Missions such as Rosetta — the first spacecraft to orbit a comet’s nucleus — play a vital role in deepening our understanding of the objects in our Solar System that could pose some risk. ESA’s planned Hera mission to a binary asteroid to test asteroid deflection will be an important step in doing something about them.

#PlanetaryDefence

This stunning image was taken on 9 September 2018 by Greg Ruppel, at his robotic observatory in Animas, New Mexico. For more of Greg’s images of Comet 21P/Giacobini-Zinner, and more, visit his website.

The Origin of the Perseids

Ever wonder where the Perseids come from? Wonder no more because this is Comet Swift-Tuttle and it is the origin of the Perseids showers.

I have been stymied in my viewing thanks to persistent clouds. In the few breaks I have managed to see a few meteors. Yesterday morning mostly, trying to watch the meteors and the launch of the Parker Space Probe (from the outside and through a window) at the same time.

Here’s ESA’s caption for the image above (E.E. Barnard/Internet Archive ):Comet Swift–Tuttle, formally 109P/Swift–Tuttle, is an enormous, icy comet on a 133 year orbit around the Sun, and the reason for the spectacular annual Perseids meteor showers on Earth.

This image shows the comet photographed on 4 April 1892 (top) and 6 April 1892 (bottom) by Professor EE Barnard, taken from Plate III in A Popular History of Astronomy in the nineteenth century by Agnes M Clerke (third edition), courtesy of Internet Archive.

Once a year, Earth passes through a section of Swift–Tuttle’s cometary tail — a cloud of particles ejected from the comet, most of which have been in this formation for a thousand years. As these tiny particles enter Earth’s atmosphere at extremely fast speeds, they burn up, resulting in the wonderful show that is a meteor shower.

Every year from the middle of July to late August, observers are treated to the spectacle of glowing cosmic debris, streaming across the night’s skies. This year the shower will peak from the evening of Sunday 12 August to the early hours of Monday 13 August. The Moon will be a new crescent moon, fortunately setting before the show really gets underway and so leaving the skies dark for what is set to be the best shower of 2018.

Discovered in 1862, the ‘near-Earth comet’ Swift–Tuttle has a nucleus 26 km in diameter — that’s two-and-a-half times the size of the asteroid that wiped out the dinosaurs, and it is travelling four times as fast.

As the largest Solar System object (bar the Moon) to repeatedly pass close to Earth, comet Swift-Tuttle’s movements have been meticulously studied by scientists around the globe. It’s most recent ‘perihelion’ — the point in its orbit in which it comes closest to the Sun — was in 1992, and the next won’t be until 12 July 2126.

Fortunately all of comet Swift–Tuttle’s orbits for the next 2000 years have been intricately calculated, when Earth is 100% safe – passing for example 22.9 million km from Earth in 2126 and 22 million km in 2261.

A close encounter is expected around 15 September 4479, when Swift-Tuttle is expected to pass within 1.6 million km of Earth — more than 90 times closer than the Sun, or, only about four times the distance of the Moon.

So, for the foreseeable future we will continue to enjoy the beautiful show put on every year by the remnants of this Sun-grazer’s historic journeys to the centre of our Solar System. These stunning events also serve as a reminder that our planet has been visited before by huge cosmic space-rocks, and has the potential to be once again.

Comet 45P Is Kind of Odd

This great image shows Comet 45P/Honda-Mrkos-Pajdušáková as seen from Africa. The image was captured by Gerald Rhemann using a telescope on December 22 from Farm Tivoli in Namibia, Africa. Very nice and very nice dark skies!  Click the image for a larger version.

Astronomers in Hawaii used the iSHELL high-resolution spectrograph to see what they could find out about 45P and what they found was not what they might have expected.

NASA — When comet 45P zipped past Earth early in 2017, researchers observing from NASA’s Infrared Telescope Facility, or IRTF, in Hawaii gave the long-time trekker a thorough astronomical checkup. The results help fill in crucial details about ices in Jupiter-family comets and reveal that quirky 45P doesn’t quite match any comet studied so far.

Like a doctor recording vital signs, the team measured the levels of nine gases released from the icy nucleus into the comet’s thin atmosphere, or coma. Several of these gases supply building blocks for amino acids, sugars and other biologically relevant molecules. Of particular interest were carbon monoxide and methane, which are so hard to detect in Jupiter-family comets that they’ve only been studied a few times before.

The gases all originate from the hodgepodge of ices, rock and dust that make up the nucleus. These native ices are thought to hold clues to the comet’s history and how it has been aging.

“Comets retain a record of conditions from the early solar system, but astronomers think some comets might preserve that history more completely than others,” said Michael DiSanti, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the new study in the Astronomical Journal.

The comet—officially named 45P/Honda-Mrkos-Pajdušáková—belongs to the Jupiter family of comets, frequent orbiters that loop around the Sun about every five to seven years. Much less is known about native ices in this group than in the long-haul comets from the Oort Cloud.
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Hubble Spots Comet C/2017 K2

An inbound comet and a record breaker, comet C/2017 K2 PANSTARRS (K2) is still a LONG ways out, perihelion in 2022.

More about C/2017 K2 PANSTARRS (K2).

Thanks to NASA, ESA, and D. Jewitt (UCLA):

A solitary frozen traveler has been journeying for millions of years toward the heart of our planetary system. The wayward vagabond, a city-sized snowball of ice and dust called a comet, was gravitationally kicked out of the Oort Cloud, its frigid home at the outskirts of the solar system. This region is a vast comet storehouse, composed of icy leftover building blocks from the construction of the planets 4.6 billion years ago.

The comet is so small, faint, and far away that it eluded detection. Finally, in May 2017, astronomers using the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Hawaii spotted the solitary intruder at a whopping 1.5 billion miles away – between the orbits of Saturn and Uranus. The Hubble Space Telescope was enlisted to take close-up views of the comet, called C/2017 K2 PANSTARRS (K2).

The comet is record-breaking because it is already becoming active under the feeble glow of the distant Sun. Astronomers have never seen an active inbound comet this far out, where sunlight is merely 1/225th its brightness as seen from Earth. Temperatures, correspondingly, are at a minus 440 degrees Fahrenheit. Even at such bone-chilling temperatures, a mix of ancient ices on the surface – oxygen, nitrogen, carbon dioxide, and carbon monoxide – is beginning to sublimate and shed as dust. This material balloons into a vast 80,000-mile-wide halo of dust, called a coma, enveloping the solid nucleus.

Astronomers will continue to study K2 as it travels into the inner solar system, making its closest approach to the Sun in 2022.

Doomed Comets

Comets coming close to (but not actually impacting) the Earth are very cool. Comets getting too close to the sun are doomed and we get to see them thanks to our space based observatories.

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.

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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!

Image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

45P/Honda-Mrkos-Pajdusakova

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.

neowisecomet2

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.