Comet 45P is seen here on Feb. 8, 2017. The comet appears very spread out and diffuse. While its overall brightness is about magnitude +8.5, the comet appears diffuse and faint. Credit: Chris Schur
This animation of comet 45P/H-M-P is composed of thirteen delay-Doppler images made during 2 hours of observation using the Arecibo Observatory on Feb. 12. Credit: USRA
Comets hide their central engines well. From Earth, we see a bright, fuzzy coma and a tail or two. But the nucleus, the source of all the hubbub, remains deeply camouflaged by dust, at best appearing like a blurry star.
To see one up close, you need to send a spacecraft right into the comet’s coma and risk getting. Or you can do the job much more cheaply by bouncing radio waves off the nucleus and studying the returning echoes to create a shadowy image.
Although crude compared to optical photos of moons and planets, radar images reveal much about an asteroid including surface details like mountains, craters, shape and rotation rate. They’re also far superior to what optical telescopes can resolve when it comes to asteroids, which, as their name implies, appear star-like or nearly so in even large professional telescopes.
On Feb. 11, green-glowing comet 45P/Honda-Mrkos-Pajdusakova, made an unusually close pass of Earth, zipping just 7.7 million miles away. Astronomers made the most of the encounter by pressing the huge 1,000-foot-wide (305 meters) Arecibo radio dish into service to image the comet’s nucleus during and after closest approach.
Arecibo Observatory, the world’s biggest single dish radio telescope, was and is still being used to image comet 45P/H-M-P. Courtesy of the NAIC – Arecibo Observatory, a facility of the NSF
“The Arecibo Observatory planetary radar system can pierce through the comet’s coma and allows us to study the surface properties, size, shape, rotation, and geology of the comet nucleus”, said Dr. Patrick Taylor, USRA Scientist and Group Lead for Planetary Radar at Arecibo.
The two lobes of comet 67P/C-G stand out clearly in this photo taken by ESA’s Rosetta spacecraft while in orbit about the comet on March 6, 2015. Credit: ESA/Rosetta
Does the shape ring a bell? Remember Rubber Ducky? It doesn’t take a rocket scientist to see that the comet’s heart resembles the twin-lobed comet 67P/Churyumov-Gerasimenko orbited by ESA’s Rosetta spacecraft. Using the dish, astronomers have seen bright regions and structures on the comet; they also discovered that the nucleus is a little larger than expected with a diameter of 0.8 mile (1.3 km) and rotates about once every 7.6 hours. Go to bed at 10 and wake up at 6 and the comet will have made one complete turn.
Comet 45P is seen here on Feb. 8, 2017. While its overall brightness is about magnitude +8.5, the comet appears diffuse and rather faint. From dark skies, it remains a binocular object at least for a little while. Credit: Chris Schur
Radio observations of 45P/H-M-P will continue through Feb. 17. Right now, the comet is happily back in the evening sky and still visible with 10×50 or larger binoculars around 10-11 p.m. local time in the east. I spotted it low in Bootes last night about 15 minutes before moonrise under excellent, dark sky conditions. It looked like a faint, smoky ball nearly as big as the full moon or about 30 arc minutes across.
This week, the pale green blob (the green’s from fluorescing carbon), vaults upward from Bootes, crosses Canes Venatici and zooms into Coma Berenices. For maps to help you track and find it night by night, please click here. I suggest larger binoculars 50mm and up or a 6-inch or larger telescope. Be sure to use low power — the comet’s so big, you need a wide field of view to get dark sky around it in order to see it more clearly.
Very few comets pass near Earth compared to the number of asteroids that routinely do. That’s one reason 45P is only the seventh imaged using radar; rarely are we treated to such detailed views!
A recent image of Comet 45P from February 4th. Image credit and copyright: Hisayoshi Kato.
A recent image of Comet 45P from February 4th. Image credit and copyright: Hisayoshi Kato.
Hankering for some cometary action? An interplanetary interloper pays us a visit this weekend, sliding swiftly through the pre-dawn northern hemisphere sky.
If you’ve never caught sight of periodic comet 45/P Honda-Mrkos-Pajdušáková, this week is a good time to try. Currently shining at magnitude +6.5, the comet makes a close 0.08 AU (7.4 million miles or 12.3 million kilometers) pass near the Earth on Saturday, February 11, at 14:44 Universal Time (UT) or 9:44 AM Eastern Standard Time. This is the closest passage of the comet for the remainder of this century, and with the Moon also reaching Full this weekend, the time to track down this comet is now.
The path of Comet 45/P through Monday, February 13th. Credit: Starry Night Edu.
We wrote about the first act for this comet last December, and Bob King also wrote up a preview last month. The comet passed perihelion 0.53 AU (49.3 million miles/ 82.1 million kilometers) from the Sun on New Year’s Eve 2016, reemerging into the dawn sky. It’s now on a swift sprint through the constellation Ophiuchus, and will cross Hercules at closest approach and into Corona Borealis and Boötes in just one week. At its closest, it’ll be moving at a whooping 23 arc minutes per hour, about three-quarters the diameter of a Full Moon!
The position of Comet 45/P as seen from latitude 30 degrees north at 4 AM. Credit: Stellarium.
At closest approach, the comet may just top naked eye brightness under dark skies at +6 magnitude.
Independently discovered by three observers worldwide in late 1948, Comet 45/P Honda-Mrkos-Pajdušáková orbits the Sun once every 5.25 years. The cumbersome name is often abbreviated as “Comet 45P HMP” or sometimes simply “Comet 45P.” The comet actually passed close enough back in 2011 for Arecibo radar to ping it, one of the very few comets to do so.
Not all apparitions of a given comet are equal, and most passages of Comet 45P were and will be uneventful. Dr. P. Clay Sharrod of the Arkansas Sky Observatory recently wrote a great account of the 1974 passage of Comet 45P, hearkening back to the same year when we were all awaiting Comet Kohoutek and Comet West was yet to come. This account might also hint at what could be in store for comet hunters this weekend.
A sketch of Comet 45P from December 10th, 1974. Image credit and copyright: Dr P. Clay Sherrod.
We managed to nab Comet 45P for the first time this AM from central Florida, though its still a tough catch. Shining at magnitude +7.5, we wouldn’t have otherwise noticed it as we swept along with our trusty Canon 15×45 image-stabilized binocs. Star-hopping finally brought us to the comet, a little fuzzy ‘star’ that stubbornly refused to snap into focus.
Comet 45P from early January, post-perihelion. Image credit and copyright: Sharin Ahmad (@shahgazer).
Unfortunately, the Moon reaches Full on Friday night, entering into the dawn sky this weekend. I’d advise hunting for the comet on every clear morning leading up to this weekend as the comet vaults northward into the pre-dawn sky. Friday night’s subtle penumbral eclipse won’t help much by way of dimming the Moon, though you can always place a house or hill between yourself and the Moon in a bid to block it out and aid in your cometary quest. There’s also a great photo op on February 16, when Comet 45P passes less than three degrees from the globular cluster M3.
As close shaves go, this passage of Comet 45P ranks as the 21st closest recorded passage of a comet near the Earth. The record goes to Comet Lexell, which passed just 0.0151 AU (1.4 million miles, or just under six times the distance to the Moon) past the Earth on July 1st, 1770. At its closest, Lexell had a visible coma spanning more than two degrees, more than four times the diameter of a Full Moon. In recent times, the last close passage of a comet other than 45P was Comet IRAS-Araki-Alcock, which zipped 0.063 AU past the Earth on June 12, 1983.
Ah, those were the days… a depiction of the Great Comet of 1769 as seen from Amsterdam, just one year (!) prior to the passage of Lexell’s Comet. Image in the Public Domain.
The gambler’s fallacy would say we’re due for the next big bright comet, though the universe seems to stubbornly refuse to roll the dice. In addition to 45P, 2017 does host a string of binocular comets, including Comet 2P Encke (March), Comet 41P/Tuttle-Giacobini-Kresák (April), Comet C/2015 ER61 PanSTARRS (May), and Comet C/2015 V2 Johnson (June). These are all explored in detail in our free e-book guide to the year, 101 Astronomical Events for 2017 out from Universe Today.
Stay warm on your comet vigil, and let us know of those observational tales of tribulation and triumph.
Artist's concept of the Wide-field Infrared Survey Explorer as its orbit around Earth. Credit: NASA/JPL
NASA’s Wide-field Infrared Survey Explorer (WISE) accomplished much during its first mission, which ran from December of 2009 to September of 2010. During the many months that it was active, the orbital telescope conducted an all-sky astronomical survey in the infrared band and discovered thousands of minor planets and numerous star clusters.
The extension of its mission, NEOWISE, has brought new life to the telescope as a comet and asteroid hunter. And since its re-activation in December of 2013, the orbiting telescope has spotted hundreds of Near Earth Objects (NEOs) and thousands of Main Belt asteroids. Most recently, it has detected two new objects (both possibly comets) which could be observable from Earth very soon.
The most recent object to be detected – 2016 WF9 – was first observed by NEOWISE on November 27th, 2016. This comet’s path through the Solar System takes it on a circuitous route, taking it from Jupiter to just inside the orbit of Earth over the course of 4.9 years. Much like other objects of its kind, 2016 WF9 may have once been a comet, or part of a population of dark objects in the Main Asteroid Belt.
Artist’s rendition of the comet 2016 WF9 as it passes Jupiter’s orbit and moves toward the sun. Credit: NASA/JPL-Caltech
In any case, 2016 WF9 will approach Earth’s orbit on February 25th, 2017, passing Earth at a minimum distance of almost 51 million km (32 million mi). This will place it well outside the orbit of the Moon, so the odds of it threatening Earth are negligible. But for those keen observers hoping to catch sight of the object, it will be close enough that it might be visible with just a pair of binoculars.
Since its discovery, 2016 WF9 has been of interest to astronomers, mainly because it straddles the already blurry line between asteroids and comets. While its proportions are known – roughly 0.5 to 1 kilometer in diameter (0.3 to 0.6 miles) – its other characteristics have led to some confusion as to where it came from. For one, its appearance (which is quite dark) and its orbit are consistent with what one expects from a comet.
But on the other hand, it lacks the characteristic cloud of dust and gas that comets are known for. As James Bauer, NEOWISE’s Deputy Principal Investigator at JPL, said in a NASA press release:
“2016 WF9 could have cometary origins. 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.”
Graphic showing the asteroids and comets observed by NASA’s Near-Earth Object Wide-field Survey Explorer (NEOWISE) mission. Credit: NASA/JPL-Caltech/UCLA/JHU
The other object, C/2016 U1 NEOWISE, was discovered about a month prior to 2016 WF9. Its orbit, which can you see by checking out the 3D Solar System Simulator, takes it from the outer Solar System to within Mercury’s orbit over the course of thousands of years. According to NASA scientists, this object is very clearly a comet, as evidenced by the dust it has been releasing as it gets closer to our Sun.
During the first week of 2017, comet C/2016 U1 NEOWISE is also likely to be visible in the night sky – in this case, in the southeastern sky shortly before dawn (for those looking from the northern hemisphere). It will reach its closest point to the Sun on January 14th (where it will be passing within Mercury’s orbit) before heading back out towards the outer Solar System.
Once again, it is believed that comet-hunters should be able to see it, though that is open to question. Paul Chodas, the manager of NASA’s Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory, thinks that this object “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.”
A mosaic of the images covering the entire sky as observed by the Wide-field Infrared Survey Explorer (WISE), part of its All-Sky Data Release. Credit: NASA/JPL
In any case, NASA will be continuing to monitor 2016 WF9 to see if they can’t sort out what it is. Should it prove to be a comet, it would be the tenth discovered by NEOWISE since it was reactivated in December of 2013. If it turns out to be an asteroid, it would be the one-hundredth discovered since its reactivation.
As of November 2016, the orbital telescope has conducted over 562,000 infrared measurements have been made of 24,024 different solar system objects, including 613 NEOs and 110 comets. It has also been responsible for discovering 249 new near-Earth objects and comets, as well as more than 34,000 asteroids during its original mission.
At present, NEOWISE’s science team is currently reprocessing all its primary mission data to extend the search for asteroids and comets. It is hoped that by taking advantage of the latest in photometric and astrometric calibrations, they will be able to push the limits of what the telescope can detect, thereby adding many more minor planets and objects to its suite of discoveries.
And be sure to enjoy this video, detailing the first two years of asteroid data collected by the NEOWISE mission:
45P/H-M-P displays a colorful coma and long ion tail on Dec. 22, 2016. Credit: Gerald Rhemann
Comet 45P/Honda-Mrkos-Pajdusakova captured in its glory on Dec. 22, 2016. It displays a bright, well-condensed blue-green coma and long ion or gas tail pointing east. Comet observers take note: a Swan Band filter shows a larger coma and increases the comet’s contrast. Credit: Gerald Rhemann
Merry Christmas and Happy Holidays all! I hope the day finds you in the company of family or friends and feeling at peace. While we’ve been shopping for gifts the past few weeks, a returning comet has been brightening up in the evening sky. Named 45P/Honda-Mrkos-Pajdusakova, it returns to the hood every 5.25 years after vacationing beyond the planet Jupiter. It’s tempting to blow by the name and see only a jumble of letters, but let’s try to pronounce it: HON-da — MUR-Koz — PIE-doo-sha-ko-vah. Not too hard, right?
Tonight, the comet will appear about 12. 5 degrees to the west of Venus in central Capricornus. You can spot it near the end of evening twilight. Use larger binoculars or a telescope. Stellarium
Comet 45P is a short period comet — one with an orbital period of fewer than 200 years — discovered on December 3, 1948 by Minoru Honda along with co-discoverers Antonin Mrkos and Ludmila Pajdusakova. Three names are the maximum a comet can have even if 15 people simultaneously discover it. 45P has a history of brightening rapidly as it approaches the sun, and this go-round is proof. A faint nothing a few weeks back, the comet’s now magnitude +7.5 and visible in 50mm or larger binoculars from low light pollution locations.
You can catch it right around the end of dusk this week and next as it arcs across central Capricornus not far behind the brilliant planet Venus. 45P will look like a dim, fuzzy star in binoculars, but if you can get a telescope on it, you’ll see a fluffy, round coma, a bright, star-like center and perhaps even a faint spike of a tail sticking out to the east. Time exposure photos reveal a tail at least 3° long and a gorgeous, aqua-tinted coma. I saw the color straight off when observing the comet several nights ago in my 15-inch reflector at low power (64x).
Use this map to help you follow the comet night to night. Tick marks start this evening (Dec. 25) and show its nightly position through Jan. 8 around 6 p.m. local time or about an hour and 15 minutes after sunset. Venus, at upper left, is shown through the 28th with stars to magnitude +7. Click the chart for a larger version you can save and print out for use at your telescope. Created with Chris Marriott’s SkyMap software
Right now, and for the remainder of its evening apparition, 45P will never appear very high in the southwestern sky. Look for it a little before the end of evening twilight, when the sky is reasonably dark and the comet is as high as it gets — about a fist above the horizon as seen from mid-northern latitudes. That’s pretty low, so make the best of your time. I recommend you being around 1 hour 15 minutes after sunset.
The further south you live, the higher 45P will appear. To a point. It hovers low at nightfall this month and next. That will change in February when the comet pulls away from the sun and makes a very close approach to the Earth while sailing across the morning sky.
How about a helping hand? On New Year’s Eve, the 2-day-old crescent Moon will be just a few degrees from 45P. This simulation shows the view through 50mm or larger binoculars with an ~6 degree field of view for the Central time zone. Map: Bob King, Source: Stellarium
45P reaches perihelion or closest distance to the sun on Dec. 31 and will remain visible through about Jan. 15 at dusk. An approximately 2-week hiatus follows, when it’s lost in the twilight glow. Then in early February, the comet reappears at dawn and races across Aquila and Hercules, zipping closest to Earth on Feb. 11 at a distance of only 7.7 million miles. During that time, we may even be able to see this little fuzzball with the naked eye; its predicted magnitude of +6 at maximum is right at the naked eye limit. Even in suburban skies, it will make an easy catch in binoculars then.
I’ll update with new charts as we approach that time, plus you can check out this earlier post by fellow Universe Today writer David Dickinson. For now, enjoy the prospect of ‘opening up’ this cometary gift as the last glow of dusk subsides into night.
A partial solar eclipse rising over the VAB. Image by author.
It’s that time of year again… time to look ahead at the top 101 astronomical events for the coming year.
And this year ’round, we finally took the plunge. After years of considering it, we took the next logical step in 2017 and expanded our yearly 101 Astronomical Events for the coming year into a full-fledged guide book, soon to be offered here for free download on Universe Today in the coming weeks. Hard to believe, we’ve been doing this look ahead in one form or another now since 2009.
This “blog post that takes six months to write” will be expanded into a full-fledged book. But the core idea is the same: the year in astronomy, distilled down into the very 101 best events worldwide. You will find the best occultations, bright comets, eclipses and much more. Each event will be interspersed with not only the ‘whens’ and ‘wheres,’ but fun facts, astronomical history, and heck, even a dash of astronomical poetry here and there.
It was our goal to take this beyond the realm of a simple almanac or Top 10 listicle, to something unique and special. Think of it as a cross between two classics we loved as a kid, Burnham’s Celestial Handbook and Guy Ottewell’s Astronomical Calendar, done up in as guide to the coming year in chronological format. Both references still reside on our desk, even in this age of digitization.
And we’ve incorporated reader feedback from over the years to make this forthcoming guide something special. Events will be laid out in chronological order, along with a quick-list for reference at the end. Each event is listed as a one- or two-page standalone entry, ready to be individually printed off as needed. We will also include 10 feature stories and true tales of astronomy. Some of these were culled from the Universe Today archives, while others are new astronomical tales written just for the guide.
Don’t miss 2017’s only total solar eclipse, crossing the United States! Image credit: Michael Zeiler/The Great American Eclipse.
The Best of the Best
Here’s a preview of some of the highlights for 2017:
-Solar cycle #24 begins to ebb in 2017. Are we heading towards yet another profound solar minimum?
-Brilliant Venus reaches greatest elongation in January and rules the dusk sky.
-45P/Honda-Mrkos-Pajdusakova passes 0.08 AU from Earth on February 11th, its closest passage for the remainder of the century.
-An annular solar eclipse spanning Africa and South America occurs on February 26th.
A sample occultation map from the book. Image credit: Occult 4.1.2.
-A fine occultation of Aldebaran by the Moon on March 5th for North America… plus more occultations of the star worldwide during each lunation.
-A complex grouping of Mercury, Venus, Mars and the Moon in mid-September.
-Saturn’s rings at their widest for the decade.
Getting wider… the changing face of Saturn’s rings. Image credit and copyright: Andrew Symes (@FailedProtostar).
-A fine occultation of Regulus for North America on October 15th, with occultations of the star by the Moon during every lunation for 2017.
-Asteroid 335 Roberta occults a +3rd magnitude star for northern Australia…
And that’s just for starters. Entries also cover greatest elongations for the inner planets and oppositions for the outer worlds, the very best asteroid occultations of bright stars, along with a brief look ahead at 2018.
Get ready for another great year of skywatching!
And as another teaser, here’s a link to a Google Calendar download of said events, complied by Chris Becke (@BeckePhysics). Thanks Chris!
Comet 2012 S1 ISON in outburst, seen on November 15, 2013. Credit and copyright: Damian Peach.
Establishing a sustained human presence somewhere other than Earth is a vital part of humanity’s future, no matter what. We know that Earth won’t last forever. We don’t know exactly which one of the many threats that Earth faces will ultimately extinguish life here, but life will be extinguished completely at some future point.
Colonizing moons or planets is one way to do it. But that’s really hard. We may make it to Mars before too long, but we don’t know how successful we’ll be at establishing a presence there. There are an awful lot of ‘ifs’ when it comes to Mars.
The only other option is space habitats. That makes sense; there’s much more space out there than there is surface area on planets and moons. And space habitats have been on the minds of thinkers, writers, and scientists for a long time.
Gerard K. O’Neill is probably the most well-known thinker when it comes to space habitats. In 1977 he published the seminal book on space habitats, called “The High Frontier: Human Colonies in Space.” O’Neill in his time popularized what is now called the “O’Neill Cylinder.”
The O’Neill Cylinder
Interior view of an O’Neill Cylinder. There are alternating strips of livable surface and “windows” to let light in. Image: Rick Guidice, NASA Ames Research Center
The O’Neill Cylinder lay the groundwork for space habitat design. It consisted of two counter-rotating cylinders, one nested inside the other. The counter-rotation provided stability and gravity. The atmosphere would be controlled, and the habitat would be powered by solar, and perhaps fusion.
An illustration of two O’Neill Cylinder’s. Image: Rick Guidice NASA Ames Research Center
The McKendree Cylinder
Other designs from other people followed O’Neill’s. Notable among them is the McKendree Cylinder. The McKendree would be gargantuan compared to the O’Neill Cylinder. Thanks to carbon nanotubes, it would have more surface area than the United States. It was designed by NASA Engineer Tom McKendree and introduced in the year 2,000 at the NASA “Turning Goals into Reality Conference.”
There’ve been other ideas for massive, high-tech space habitats, including the Bernal Sphere and the Stanford Torus. All of these designs are typical of engineers and technologists. Lots of high-tech, lots of steel, lots of machinery. But the engineers and scientists behind those designs weren’t the only ones thinking about humans in space.
Carl Sagan was too. And he had a very different idea of what space habitats could be.
So Crazy It Just Might Work
But the craziest idea for space habitats has got to be Carl Sagan’s, from his 1985 book “Comet.”In “Comet” Sagan suggested that humans could seek refuge in, and even colonize, actual comets travelling through our Solar System. Using all the advanced technologies thought about in Sagan’s time—but which don’t exist yet—comets could be transformed into humanity’s salvation. His idea is a world apart from the high-tech, highly-engineered, gleaming habitat designs that most people think of when they think of space habitats.
I’m a fan of Sagan’s. Like many in my generation, I was influenced by his TV series Cosmos. I loved it and it’s stuck with me. His book “The Demon-Haunted World” taught us what scientific skepticism can be, and how useful it is.
“Comet” was published only months before Halley’s Comet arrived in our inner Solar System in 1986. Image: Jon Lomberg, Random House New York.
Sagan’s is the most surprising—and perhaps bleakest—view of space habitats. Life inside comets sounds shocking, and maybe even foolish, but as Sagan explains, there is some reasoning behind the idea.
Remember that when Sagan wrote about this, thermonuclear war between the superpowers was a “thing,” and thinkers like Sagan felt a sense of imminent danger. That sense of foreboding may have contributed to his “comets-as-space-habitas” idea. Plus, he was just an innovative thinker.
Carl Sagan in 1980.
Sagan’s thinking behind using comets as space habitats starts out something like this: if there are about a hundred thousand comets crossing Earth’s orbit, and another hundred trillion in the Oort Cloud, their combined surface area is roughly equal to about a hundred million Earths. And with advanced technology, Sagan proposed that these comets could be captured and colonized and sent on orbits and trajectories desirable to humans.
Comet Lovejoy and its spectacular “lively” ion tail photographed on January 8th by Nick Howes at Tzec Muan Network at Siding Spring Australia. Could Lovejoy and its brethren one day provide a home for humanity?
Comets are rich in minerals, water ice, and biological compounds. Or so it was thought at the time. That means raw material for manufacturing, water to drink and to supply oxygen, biological compounds for bio-engineering, and even the raw material for rocket fuel. Add a fusion reactor for power, and
comets could end up being the convenience stores of the Solar System.
Physicist Freeman Dyson, an innovative thinker himself, had something to add to Sagan’s comet idea. In “Comet,” Sagan tells of Dyson’s ideas around genetic engineering, and that one day we should be able to engineer forms of life that could thrive on comets, and meet some of our needs. Dyson talks about a giant, genetically engineered tree that could grow on a comet, planted in snow rich in organic chemicals. The tree would supply us with fresh oxygen.
The OSIRIS narrow-angle camera aboard the Rosetta spacecraft captured this image of comet 67P/Churyumov-Gerasimenko on September 30, 2016. Does it look habitable, or potentially habitable, to you? Credits: ESA/Rosetta/MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
This sounds extremely far-fetched: humans living inside comets travelling through space, with giant genetically engineered trees and fusion power plants. I try to remind myself that many things we take for granted now were once thought to be laughable. But even though parts of the comet-as-space-habitat idea sound fanciful—like the giant tree—there may be the seed of a practical idea here, with humans hitching rides on comets, molding them to our purposes, and extracting resources like minerals and fuel from them.
High cliffs on the surface of Comet Churyumov–Gerasimenko as imaged by the Rosetta spacecraft. Image Credit & Licence (CC BY-SA 3.0 IGO): ESA, Rosetta spacecraft, NAVCAM; Additional Processing: Stuart Atkinson
Sagan was an agile creative thinker. He’s clearly riffing when he outlines his ideas for life on comets. He’s like the John Coltrane of space science.
It seems doubtful that we would go to the trouble to turn comets into actual habitats. It’s probably more science fiction that science. But the future is unwritten, and given enough time, almost anything might be possible.
Comet 45P/Honda-Mrkos-Pajdušáková From October 1st, 2011 taken with a 10"/3.8 Newtonian and CCD imager. Image credit and copyright: Michael Jäger.
Looking for a good binocular comet? Well, if luck is on our side, we should be getting our first looks at periodic Comet 45P/Honda-Mrkos-Pajdušáková as it tops +10th magnitude in dusk skies over the next few weeks.
The swift path of Comet 45P/Honda-Mrkos-Pajdušáková on the nights of February 9th to February 12th. Image credit: Starry Night.
Comet 45P/Honda-Mrkos-Pajdušáková is expected to reach maximum brightness around late February 2017. Discovered independently by astronomers Minoru Honda, Antonin Mrkos and L’udmila Pajdušáková on December 3rd, 1948, Comet 45P/Honda-Mrkos-Pajdušáková orbits the Sun once every 5.25 years on a short period orbit. Comet 45P/Honda-Mrkos-Pajdušáková is set to break binocular +10th magnitude brightness in mid-December 2017, and may reach a maximum brightness of magnitude +7 from January through February 2017.
Slovak astronomer ?udmila Pajdušáková, co-discoverer of 5 comets, including Comet 45P/Honda-Mrkos-Pajdušáková. Image credit: The Skalnaté Pleso Observatory.
Currently and through the end of 2016, the comet sits towards the center of the Milky Way Galaxy in Sagittarius at a faint +15th magnitude in the evening sky. The comet may break +10th magnitude and become very briefly visible in the first few weeks of December before getting too close to the Sun to observe in late 2016 and crossing into the morning sky in early 2017.
The path of Comet 45/P from mid-November through December 15th, 2016. Image credit: Starry Night.
Visibility prospects: At its brightest, Comet 45P/Honda-Mrkos-Pajdušáková will be passing through the constellation Hercules during closest approach on February 11th. The comet then passes through the constellations of Corona Borealis, Boötes, Canes Venatici, Ursa Major into Leo through to the end of February as it recedes. In the second week of February, the comet is visible in the dawn sky 82 degrees west of the Sun at maximum brightness. This apparition favors the northern hemisphere. The comet will reach perihelion on December 29th, 2016 at 0.53 Astronomical Units (AU) from the Sun, and the comet passes just 0.08 AU (7.4 million miles) from the Earth on February 11th at 14:44 UT. The comet made a slightly closer pass in 2011, and was a fine binocular object that time around. At its closest, the comet will cross nine degrees of sky from one night to the next. Some notable dates for comet 45P/Honda-Mrkos-Pajdušáková are:
November 23rd: Venus passes 6′ from the comet.
December 12th: May break 10th magnitude.
December 14th: Passes near M75.
December 15th: Crosses into the constellation Capricornus.
January 4th: Passes near the +4th magnitude star Theta Capricorni
January 10th: Crosses the ecliptic northward.
January 16th: Passes into Aquarius.
January 22nd: Passes near NGC 7009, M72 and M73.
January 25th: Passes 8 degrees from the Sun and into the dawn sky.
January 28th: Crosses into Aquila.
February 3rd: Crosses the celestial equator northward.
February 4th: Passes 4′ from the star +3.3 magnitude star Delta Aquilae.
February 6th: Crosses the Galactic equator.
February 7th: Crosses into Ophiuchus.
February 9th: Crosses into Hercules.
February 16th: makes a wide pass near M3.
February 19th: Drops back below +10th magnitude.
The path of Comet 45P/Honda-Mrkos-Pajdušáková through the inner solar system. Image credit: NASA/JPL.
This is the final close (less than 0.1 AU) passage of Comet 45P/Honda-Mrkos-Pajdušáková near the Earth for this century.
On July 1st 1770, Comet D/1770 L1 Lexell passed 0.0151AU from the Earth; a comet in 1491 may have passed closer. Next year’s passage of 45P/Honda-Mrkos-Pajdušáková ranks as the 21st closest passage of a comet near the Earth.
Why do comets end up with such cumbersome names? Well, comets derive their names from the first three discovers that submit the find within a 24 hour period to the Minor Planet Center’s Central Bereau for Astronomical Telegrams, which, in fact, received its last ‘telegram’ during the discovery of Comet Hale-Bopp around two decades ago. Increasingly, comets are receiving names of all sky surveys such as LINEAR and PanSTARRS from robotic competition against amateur hunters. It does seem like you need an umlaut or the chemical symbol for boron to in your moniker to qualify these days… rare is the ‘Comet Smith.’ But hey, it’s still fun to watch science journalists try and spell the Icelandic volcano Eyjafjallajökull and comet Churyumov-Gerasimenko over and over… Perhaps, we should insist that our first comet discovery is actually spelled Comet Dîckînsðn…
And Comet 45/P is just one of the fine binocular comets on deck for 2017. We’re also expecting Comet 41P/Tuttle-Giacobini-Kresák, 2/P Encke, C/2015 ER61 PanSTARRS Comet C/2015 V2 Johnson to break +10th magnitude next year… and the next great naked eye ‘Comet of the Century’ could light up the skies at any time.
Goldstone radar pings comet 45/P back in 2011. Image credit: NASA.
Binoculars are the best tool to observe bright comets, as they allow you to simply sweep the star field and admire the full beauty of a comet, coma, tail(s) and all. Keep in mind, a comet will often appear visually fainter than its quoted brightness… this is because, like nebulae, that intrinsic magnitude is ‘smeared out’ over an extended area. To my eye, a binocular comet often looks like a fuzzy, unresolved globular cluster that stubbornly refuses to snap into focus.
Don’t miss your first looks at Comet 45/P 45P/Honda-Mrkos-Pajdušáková, as it spans 2016 into 2017.
In the distant past, the orbit of 67P/Churyumov-Gerasimenko extended far beyond Neptune into the refrigerated Kuiper Belt. Interactions with the gravitational giant Jupiter altered the comet's orbit over time, dragging it into the inner Solar System. Credit: Western University, Canada
In the distant past, the orbit of 67P/Churyumov-Gerasimenko extended far beyond Neptune into the refrigerated Kuiper Belt. Interactions with the gravitational giant Jupiter altered the comet’s orbit over time, dragging it into the inner Solar System. Credit: Western University, Canada
Rosetta’s Comet hails from a cold, dark place. Using statistical analysis and scientific computing, astronomers at Western University in Canada have charted a path that most likely pinpoints comet 67P/Churyumov-Gerasimenko’s long-ago home in the far reaches of the Kuiper Belt, a vast region beyond Neptune home to icy asteroids and comets.
According to the new research, Rosetta’s Comet is relative newcomer to the inner parts of our Solar System, having only arrived about 10,000 years ago. Prior to that, it spent the last 4.5 billion years in cold storage in a rough-and-tumble region of the Kuiper Belt called the scattered disk.
The Kuiper Belt was named in honor of Dutch-American astronomer Gerard Kuiper, who postulated a reservoir of icy bodies beyond Neptune. The first Kuiper Belt object was discovered in 1992. We now know of more than a thousand objects there, and it’s estimated it’s home to more than 100,000 asteroids and comets there over 62 miles (100 km) across. Credit: JHUAPL
In the Solar System’s youth, asteroids that strayed too close to Neptune were scattered by the encounter into the wild blue yonder of the disk. Their orbits still bear the scars of those long-ago encounters: they’re often highly-elongated (shaped like a cigar) and tilted willy-nilly from the ecliptic plane up to 40°. Because their orbits can take them hundreds of Earth-Sun distances into the deeps of space, scattered disk objects are among the coldest places in the Solar System with surface temperatures around 50° above absolute zero. Ices that glommed together to form 67P at its birth are little changed today. Primordial stuff.
Watch how Rosetta’s Comet’s orbit has evolved since the comet’s formation
There are two basic comet groups. Most comets reside in the cavernous Oort Cloud, a roughly spherical-shaped region of space between 10,000 and 100,000 AU (astronomical unit = one Earth-Sun distance) from the Sun. The other major group, the Jupiter-family comets, owes its allegiance to the powerful gravity of the giant planet Jupiter. These comets race around the Sun with periods of less than 20 years. It’s thought they originate from collisions betwixt rocky-icy asteroids in the Kuiper Belt.
Fragments flung from the collisions are perturbed by Neptune into long, cigar-shaped orbits that bring them near Jupiter, which ropes them like calves with its insatiable gravity and re-settles them into short-period orbits.
Comet 67P/Churyumov-Gerasimenko is a Jupiter-family comet. Its 6.5 year journey around the Sun takes it from just beyond the orbit of Jupiter at its most distant to between the orbits of Earth and Mars at its closest. Credit: ESA with labels by the author
Mattia Galiazzo and solar system expert Paul Wiegert, both at Western University, showed that in transit, Rosetta’s Comet likely spent millions of years in the scattered disk at about twice the distance of Neptune. The fact that it’s now a Jupiter family comet hints of a possible long-ago collision followed by gravitational interactions with Neptune and Jupiter before finally becoming an inner Solar System homebody going around the Sun every 6.45 years.
By such long paths do we arrive at our present circumstances.
The last set of images taken by the Rosetta spacecraft's NAVCAM during the final month of its mission. ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.
The Rosetta team has released the final batch of images taken by the NAVCAM during the last month of its two years of investigations at Comet 67P/Churyumov-Gerasimenko. It’s a big batch and they are absolutely stunning, but its sad to know they are the last NAVCAM images. The image set covers the period from September 2-30, 2016 when the spacecraft was on elliptical orbits that sometimes brought it to within 2 km of the comet’s surface, so you’ll see a wide variety of imagery with a variety of geology and lighting conditions.
Take a look below:
A large boulder sits precariously on Comet 67P/Churyumov-Gerasimenko as seem by Rosetta’s NAVCAM on September 11, 2016. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.
While these are the final NAVCAM images, there may be more images coming from the OSIRIS camera. Also, many other instruments will be releasing data, as they were active as long as possible before impact. Many of the science instruments were expected to return their last data from between 20 meters to 5 meters above the surface.
ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) collected data on the density of gas around the comet and its composition while GIADA (Grain Impact Analyser and Dust Accumulator) measured the dust density.
RPC’s (Rosetta Plasma Consortium) instrument suite provided a look at interaction between the solar wind and the surface of the comet. Alice, an Ultraviolet Imaging Spectrometer similar to the one on New Horizons, took high resolution ultraviolet spectra of the surface. RSI (Radio Science Investigation) got the most accurate measurements of the gravity field during descent.
A variety of geology and light on on Comet 67P/Churyumov-Gerasimenko as seem by Rosetta’s NAVCAM on September 5, 2016. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.A field of bright bolders on Comet 67P/Churyumov-Gerasimenko as seem by Rosetta’s NAVCAM during September 2-20. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.
And here’s one of the last five images from Rosetta’s NAVCAM as it descended to its controlled impact on September 30 onto Comet 67P, taking incredible, close-up images during descent, this one just 18.1 km up. It shows the “drippy icing” landscape on this portion of the comet:
Single frame enhanced NavCam image taken on September 30, 2016 at 00:27 GMT, when Rosetta was 18.1 km from the center of the nucleus of Comet 67P/Churyumov-Gerasimenko. The scale at the surface is about 1.5 m/pixel and the image measures about 1.6 km across. ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.
Rosetta’s OSIRIS narrow-angle camera captured this image of Comet 67P/Churyumov-Gerasimenko from an altitude of about 16 km above the surface during the spacecraft’s final descent on September 30, 2016. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.
With a soft “awwww” from the mission team in the control center in Darmstadt, Germany, the signal from the Rosetta spacecraft faded, indicating the end of its journey. Rosetta made a controlled impact onto Comet 67P/Churyumov–Gerasimenko, sending back incredible close-up images during descent, after two years of investigations at the comet.
“Farewell Rosetta. You have done the job. That was space science at its best,” said Patrick Martin, Rosetta mission manager.
Rosetta’s final resting spot appears to be in a region of active pits in the Ma’at region on the two-lobed, duck-shaped comet.
The information collected during the descent – as well as during the entire mission – will be studied for years. So even though the video below about the mission’s end will likely bring a tear to your eye, rest assured the mission will continue as the science from Rosetta is just getting started.
“Rosetta has entered the history books once again,” says Johann-Dietrich Wörner, ESA’s Director General. “Today we celebrate the success of a game-changing mission, one that has surpassed all our dreams and expectations, and one that continues ESA’s legacy of ‘firsts’ at comets.”
Launched in 2004, Rosetta traveled nearly 8 billion kilometers and its journey included three Earth flybys and one at Mars, and two asteroid encounters. It arrived at the comet in August 2014 after being in hibernation for 31 months.
After becoming the first spacecraft to orbit a comet, it deployed the Philae lander in November 2014. Philae sent back data for a few days before succumbing to a power loss after it unfortunately landed in a crevice and its solar panels couldn’t receive sunlight. But Rosetta continued to monitor the comet’s evolution as it made its closest approach and then moved away from the Sun. However, now Rosetta and the comet are too far away from the Sun for the spacecraft to receive enough power to continue operations.
“We’ve operated in the harsh environment of the comet for 786 days, made a number of dramatic flybys close to its surface, survived several unexpected outbursts from the comet, and recovered from two spacecraft ‘safe modes’,” said operations manager Sylvain Lodiot. “The operations in this final phase have challenged us more than ever before, but it’s a fitting end to Rosetta’s incredible adventure to follow its lander down to the comet.”
Compilation of the brightest outbursts seen at Comet 67P/Churyumov–Gerasimenko by Rosetta’s OSIRIS narrow-angle camera and Navigation Camera between July and September 2015. Credit: OSIRIS: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; NavCam: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0.
Rosetta’s Legacy and Discoveries
Of its many discoveries, Rosetta’s close-up views of the curiously-shaped Comet 67P have already changed some long-held ideas about comets. With the discovery of water with a different ‘flavor’ to that of Earth’s oceans, it appears that Earth impacts of comets like 67P/Churyumov–Gerasimenko may not have delivered as much of Earth’s water as previously thought.
From Philae, it was determined that even though organic molecules exist on the comet, they might not be the kind that can deliver the chemical prerequisites for life. However, a later study revealed that complex organic molecules exist in the dust surrounding the comet, such as the amino acid glycine, which is commonly found in proteins, and phosphorus, a key component of DNA and cell membranes. This reinforces the idea that the basic building blocks may have been delivered to Earth from an early bombardment of comets.
Rosetta’s long-term monitoring has also shown just how important the comet’s shape is in influencing its seasons, in moving dust across its surface, and in explaining the variations measured in the density and composition of the comet’s coma.
And because of Rosetta’s proximity to the comet, we all went along for the ride as the spacecraft captured views of what happens as a comet comes close to the Sun, with ice sublimating and dusty jets exploding from the surface.
Studies of the comet show it formed in a very cold region of the protoplanetary nebula when the Solar System was forming more than 4.5 billion years ago. The comet’s two lobes likely formed independently, but came together later in a low-speed collision.
“Just as the Rosetta Stone after which this mission was named was pivotal in understanding ancient language and history, the vast treasure trove of Rosetta spacecraft data is changing our view on how comets and the Solar System formed,” said project scientist Matt Taylor.
Sequence of images captured by Rosetta during its descent to the surface of Comet 67P/C-G on September 30, 2016. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.
Journey’s End
During the final hours of the mission on Friday morning, the instrument teams watched the data stream in and followed the spacecraft as it moved closer to its targeted touchdown location on the “head” of the 4km-wide comet. The pitted region where Rosetta landed appear to be the places where 67P ejects gas and dust into space, and so Rosetta’s swan song will provide more insight into the comet’s icy jets.
“With the decision to take Rosetta down to the comet’s surface, we boosted the scientific return of the mission through this last, once-in-a-lifetime operation,” said Martin. ““It’s a bittersweet ending, but … Rosetta’s destiny was set a long time ago. But its superb achievements will now remain for posterity and be used by the next generation of young scientists and engineers around the world.”
And so, my final day dawns.
Just a few grains are left to drain through
The hourglass of my life.
The Comet is a hole in the sky.
Rolling, turning, a black void churning
Silently beneath me.
Down there, waiting for me, Philae sleeps,
Its bed a cold cave floor,
A quilt of sparkling hoarfrost
Pulled over its head…
I have so little time left;
I sense Death flying behind me,
I feel his breath on my back as I look down
At Ma’at, its pits as black as tar,
A skulls’s empty eye sockets staring back
At me, daring me to leave the safety
Of this dusty sky and fly down to join them,
Never to spread my wings again; never
To soar over The Comet’s tortured pinnacles and peaks,
Or play hide and seek in its jets and plumes…
I don’t want to go.
I don’t want to be buried beneath that filthy snow.
This is wrong! I want to fly on!
There is so much more for me to see,
So much more to do –
But the end is coming soon.
All I ask of you is this: don’t let me crash.
Help me land softly, kissing the ground,
Coming to rest with barely a sound
Like a leaf falling from a tree.
Don’t let me die cartwheeling across the plain,
Wings snapping, cameras shattering,
Pieces of me scattering like shrapnel
Across the ice. Let me end my mayfly life
In peace, whole, not as debris rolling uncontrollably
Into Deir el-Medina…
It’s time to go, I know.
Only hours remain until I join Philae
And my great adventure ends
So I’ll send this and say goodbye.
If I dream, I’ll dream of Earth
Turning beneath me, bathing me in
Fifty shades of blue…
In years to come I hope you’ll think of me
And smile, remembering how, for just a while,
We explored a wonderland of ice and dust
Together, hand in hand.
