Comet C/2013 US10 Catalina photographed from high atop the Himalayas by Ajay Talwar with a 200mm lens on a tracking mount this morning Nov. 20, 2015. Credit: Ajay Talwar
If you love watching comets and live north of the equator, you’ve been holding your breath a l-o-n-g time for C/2013 US10 Catalina to make its northern debut. I’m thrilled to report the wait is over. The comet just passed perihelion on Nov. 15th and has begun its climb into morning twilight.
Map showing the sky facing southeast around the start of dawn. Comet C/2013 US10 Catalina leaps into the morning sky in eastern Virgo beginning this weekend at around magnitude +7. Comet positions are marked by small crosses every 5 days around 6 a.m. CST (12:00 Universal Time) for mid-northern latitudes (Minneapolis, specifically). Planet positions are shown for Nov. 21st. Stars to mag. +7. Source: Chris Marriott’s SkyMap
The first post-perihelion photo, taken on Nov. 19th by astrophotographer Ajay Talwar from Devasthal Observatory high in the Indian Himalayas, show it as a starry dot with a hint of a tail only 1° above the eastern horizon at mid-twilight. Additional photos made on the following mornings show the comet inching up from the eastern horizon into better view. Estimates of its current brightness range from magnitude +6.8-7.0.
Sometimes black and white is better. This is the same chart as above but in a handier version for use at the telescope. Source: Chris Marriott’s SkyMap
Talwar, who teaches astrophotography classesand is a regular contributor to The World at Night (TWAN), drove 9 hours from his home to the Himalaya mountains, then climbed up the observatory dome to get enough horizon to photograph the comet. The window of opportunity was very narrow; Talwar had only 10 minutes to bag his images before the comet was overwhelmed by zodiacal light and twilight glow. When asked if it was visible in binoculars, he thought it would be but had too little time to check despite bringing a pair along.
Ajay Talwar recorded the very first post-perihelion photo of Comet Catalina on Nov. 19th from Devasthal Observatory. Prior to perihelion, the comet was only visible from the southern hemisphere. Copyright: Ajay Talwar
A difficult object at the moment, once it frees itself from the horizon haze in about a week, Catalina should be easily visible in ordinary binoculars. Watch for it to gradually brighten through the end of the year, peaking around magnitude +5.5 — just barely naked eye — in late December and early January, when it will be well-placed high in the northeastern sky near the star Arcturus (see map). Matter of fact, on the first morning of the new year, it creeps only 1/2° southwest of the star for a splendid conjunction.
Even before perihelion, Comet Catalina was a beautiful thing. This photo was taken on October 1, 2015. Credit: Jose Chambo
Halloween 2013 was an auspicious one. That’s when Comet C/2013 US10 was first picked up by the Catalina Sky Survey. The “US10” part comes from initial observations that suggested it was an asteroid. Additional photos and observations instead revealed a fuzzy comet on a steeply tilted orbit headed for the inner Solar System after a long sojourn in the Oort Cloud.
Comet C/2013 US10 Catalina will slice through the plane of the Solar System at an angle of 149° never to return. It comes closest to Earth on Jan. 12, 2016. After that time, the comet will recede and fade. Credit: JPL Horizons
Its sunward journey has been nothing short of legendary, requiring several million years of inbound travel from the frigid fringe to the relative warmth of the inner Solar System. Catalina will pass closest to Earth on Jan. 12th at 66.9 million miles (107.7 million km) before buzzing off into interstellar space. Yes, interstellar. Perturbations by the planets have converted its orbit into a one-way ticket outta here.
Check this out! Look to the east at the start of dawn on Dec. 7th to see a remarkable pairing of comet, Venus and the waning lunar crescent with earthshine. Source: Stellarium
When using the maps above, keep in mind they show the comet’s changing position, but the constellations and planets can only be shown for the one date, Nov. 21st. Like the comet, they’ll also be slowly sliding upward in the coming days and mornings due to Earth’s revolution around the Sun; stars that are near the horizon on Nov. 21 at 5:30 or 6 a.m. will be considerably higher up in a darker sky by the same time in December. Adding the shift of the stars to that of the comet, Catalina gains about 1° of altitude per day in the coming two weeks.
When you go out to find Catalina in binoculars, note its location on the map and then use the stars as steppingstones, starting with a bright obvious one like Spica and “stepping” from there to the next until you arrive at the one closest to the comet.
I’m so looking forward to finding Catalina. Nothing like a potentially naked eye comet to warm up those cold December mornings. Mark your calendar for the morning of Dec. 7th, when this rare visitor will join Venus and the crescent Moon in the east at the start of morning twilight. See you in spirit at dawn!
Up for one more? Well, this week’s offering is a bit chancy, but we ‘may’ be in for a minor outburst from a usually quiescent shower. On any given year, the Alpha Monocerotid meteors wouldn’t rate a second look.
A confirmed 2014 Alpha Monocerotid. Image credit: The United Kingdom Meteor Observation Network (UKMON)
First, however, a caveat is in order. Meteor showers never read prognostications and often prove to be fickle, and wild card meteor storms doubly so.
Not to be confused with the straight up Monocerotids which peak in early December, the Alpha Monocerotids are moderately active from November 15th through the 25th, with a soft peak on the 22nd. And though the radiant derives its name from the brightest star in the rambling constellation of Monoceros the Unicorn, the radiant is actually located at its peak at right ascension 7 hours 46 minutes and declination +00 degrees 24 minutes, just across the border in the constellation Canis Minor.
Another bright Alpha Moncerotid meteor under a bright Moon. Image credit: UKMON
The Alpha Monocerotids have a curious history. They first caught the keen eye of observers in 1925, when F.T. Bradley watching from rural Virginia noted 37 meteors over a 13 minute span. In the 20th century, small outbursts seemed to ply the skies around November 22nd on the fifth year of each decade, with brief outbursts seen in 1935 and 1985. NASA astronomer and SETI Institute research scientist Peter Jenniskens predicted a 1995 outburst, and as predicted, a brief 30 minute display greeted members of the Dutch Meteor Society based under dark skies in southern Spain. The shower had a brief 5-minute climax in 1995, with an extrapolated zenithal hourly rate of 420.
The location of the Alpha Monocerotid meteor shower radiant at 6AM local from about 30 degrees latitude north. Image credit: Stellarium
Prospects for the shower in 2015
As of this writing, a major outburst from the Alpha Monocerotids isn’t predicted for 2015… but you just never know. It’s always worth watching for an outburst on the night of November 21/22nd, especially in years ending in five.
In 2015, the Moon phase for the night of Saturday/Sunday November 21st/22nd is waxing gibbous and about 79% illuminated and setting at around 1:00 AM local, putting it safely out of view.
The orientation of the Earth’s shadow, Moon, Sun and shower radiant at 4:00 UT, November 22nd. Image credit: Orbitron
The predicted peak for the 2015 Alpha Monocerotids is centered on 4:25 UT/11:25 PM EST as per the International Meteor Organization (IMO), favoring western European longitudes in a similar fashion as 1995 at dawn on Sunday, November 22nd.
Thus far, the source comet for the Alpha Monocerotids remains a mystery, though a prime contender is Comet C/1943 W1 van Gent-Peltier-Daimaca. Discovered during the Second World War, this comet has an undefined long period orbit, and reached perihelion 0.87 AU from the Sun on January 12th, 1944.
Jenniskens notes that orbital configurations of Jupiter and Saturn may play a role in the long term modification of meteor streams such as the Alpha Monocerotids. A fascinating discussion on predicting meteor outbursts and the evolution of meteor streams by Mr Jenniskens can be read here.
The stream seems to have a very brief burst of activity of less than an hour, reminiscent of the elusive January Quadrantids. The Alpha Monocerotid radiant sits highest in the sky at around 4 AM local, and the incoming speed of the meteors is a very respectable 65 kilometers a second, making for brief swift trails.
Meteor Watching and Reporting
But beyond just observing, many sky watchers choose to log what they see and report it. Meteor shower streams—especially obscure ones such as the Alpha Monocerotids—are often poorly understood, and observers provide a valuable service by counting and reporting the number of meteors seen over a particular period of time.
Imaging meteors is as simple as setting up a DSLR on a tripod for wide angle shots, and taking repeated exposures of the sky. We generally take a few test shots to get the ISO/f-stop mix just right for the current sky conditions, then set our intervalometer to take repeated 30-second exposures while we visually observe. Aim about 45 degrees away from the radiant to catch meteors in profile, and check the camera lens periodically for morning dew. We generally keep a hair dryer handy to combat condensation under moisture-laden Florida skies.
Maybe a vigil for an Alpha Monocerotid outburst is an exercise in hunting unicorns… but watching an outburst would be an unforgettable sight. Perhaps, the Alpha Monocerotid stream is on the wane in the 21st century… or a new outburst is still in the wings, waiting to greet dawn residents of the Earth.
Something other than a transiting planet makes the Kepler star KIC fluctuate wildly and unpredictably in brightness. Astronomers suspect a shattered comet, but who knows? Credit: NASA
“Bizarre.” “Interesting.” “Giant transit”. That were the reactions of Planet Hunters project volunteers when they got their first look at the light curve of the otherwise normal sun-like star KIC 8462852 nearly.
Of the more than 150,000 stars under constant observation during the four years of NASA’s primary Kepler Mission (2009-2013), this one stands alone for the inexplicable dips in its light. While almost certainly naturally-caused, some have suggested we consider other possibilities.
Kepler-11, a sun-like star orbited by six planets. At times, two or more planets pass in front of the star at once, as shown in this artist’s conception of a simultaneous transit of three planets observed by the Kepler spacecraft on Aug. 26, 2010. During each pass or transit, the star’s light fades in a periodic way. Credit: NASA/Tim Pyle
You’ll recall that the orbiting Kepler observatory continuously monitored stars in a fixed field of view focused on the constellations Lyra and Cygnus hoping to catch periodic dips in their light caused by transiting planets. If a drop was seen, more transits were observed to confirm the detection of a new exoplanet.
And catch it did. Kepler found 1,013 confirmed exoplanets in 440 star systems as of January 2015 with 3,199 unconfirmed candidates. Measuring the amount of light the planet temporarily “robbed” from its host star allowed astronomers to determine its diameter, while the length of time between transits yielded its orbital period.
Graph showing the big dip in brightness of KIC 8462852 around 800 days (center) followed after 1500 days whole series of dips of varying magnitude up to 22%. The usual drop in light when an exoplanet transits its host star is a fraction of a percent. The star’s normal brightness has been set to “1.00” as a baseline. Credit: Boyajian et. all
Volunteers with the Planet Hunters project, one of many citizen science programs under the umbrella of Zooniverse, harness the power of the human eye to examine Kepler light curves (a graph of a star’s changing light intensity over time), looking for repeating patterns that might indicate orbiting planets. They were the first to meet up with the perplexing KIC 8462852.
A detailed look at a small part of the star’s light curve reveals an unknown, regular variation of its light every 20 days. Superimposed on that is the star’s 0.88 day rotation period. Credit: Boyajian et. all
This magnitude +11.7 star in Cygnus, hotter and half again as big as the Sun, showed dips all over the place. Around Day 800 during Kepler’s run, it faded by 15% then resumed a steady brightness until Days 1510-1570, when it underwent a whole series of dips including one that dimmed the star by 22%. That’s huge! Consider that an exo-Earth blocks only a fraction of a percent of a star’s light; even a Jupiter-sized world, the norm among extrasolar planets, soaks up about a percent.
Exoplanets also show regular, repeatable light curves as they enter, cross and then exit the faces of their host stars. KIC 8462852’s dips are wildly a-periodic.
Could a giant comet breakup and subsequent cascading breakups of those pieces be behind KIC 8462852’s erratic changes in brightness? Credit: NASA
Whatever’s causing the flickering can’t be a planet. With great care, the researchers ruled out many possibilities: instrumental errors, starspots (like sunspots but on other stars), dust rings seen around young, evolving stars (this is an older star) and pulsations that cover a star with light-sucking dust clouds.
What about a collision between two planets? That would generate lots of material along with huge clouds of dust that could easily choke off a star’s light in rapid and irregular fashion.
A great idea except that dust absorbs light from its host star, warms up and glows in infrared light. We should be able to see this “infrared excess” if it were there, but instead KIC 8462852 beams the expected amount of infrared for a star of its class and not a jot more. There’s also no evidence in data taken by NASA’s Wide-field Infrared Survey Explorer (WISE) several years previously that a dust-releasing collision happened around the star.
Our featured star shines at magnitude +11.7 in the constellation Cygnus the Swan (Northern Cross) high in the southern sky at nightfall this month. A 6-inch or larger telescope will easily show it. Use this map to get oriented and the map below to get there. Source: Stellarium
After examining the options, the researchers concluded the best fit might be a shattered comet that continued to fragment into a cascade of smaller comets. Pretty amazing scenario. There’s still dust to account for, but not as much as other scenarios would require.
Detailed map showing stars to around magnitude 12 with the Kepler star identified. It’s located only a short distance northeast of the open cluster NGC 6886 in Cygnus. North is up. Click to enlarge. Source: Chris Marriott’s SkyMap
Being fragile types, comets can crumble all by themselves especially when passing exceptionally near the Sun as sungrazing comets are wont to do in our own Solar System. Or a passing star could disturb the host star’s Oort comet cloud and unleash a barrage of comets into the inner stellar system. It so happens that a red dwarf star lies within about 1000 a.u. (1000 times Earth’s distance from the Sun) of KIC 8462852. No one knows yet whether the star orbits the Kepler star or happens to be passing by. Either way, it’s close enough to get involved in comet flinging.
So much for “natural” explanations. Tabetha Boyajian, a postdoc at Yale, who oversees the Planet Hunters and the lead author of the paper on KIC 8462852, asked Jason Wright, an assistant professor of astronomy at Penn State, what he thought of the light curves. “Crazy” came to mind as soon he set eyes on them, but the squiggles stirred a thought. Turns out Wright had been working on a paper about detecting transiting megastructures with Kepler.
There are Dyson rings and spheres and a Dyson swarm depicted here. Could this or a variation of it be what we’re seeing around KIC 8462852? Not likely, but a fun thought experiment. Credit: Wikipedia
In a recent blog, he writes: “The idea is that if advanced alien civilizations build planet-sized megastructures — solar panels, ring worlds, telescopes, beacons, whatever — Kepler might be able to distinguish them from planets.” Let’s assume our friendly aliens want to harness the energy of their home star. They might construct enormous solar panels by the millions and send them into orbit to beam starlight down to their planet’s surface. Physicist Freeman Dyson popularized the idea back in the 1960s. Remember the Dyson Sphere, a giant hypothetical structure built to encompass a star?
From our perspective, we might see the star flicker in irregular ways as the giant panels circled about it. To illustrate this point, Wright came up with a wonderful analogy:
“The analogy I have is watching the shadows on the blinds of people outside a window passing by. If one person is going around the block on a bicycle, their shadow will appear regularly in time and shape (like a regular transiting planet). But crowds of people ambling by — both directions, fast and slow, big and large — would not have any regularity about it at all. The total light coming through the blinds might vary like — Tabby’s star.”
The Green Bank Telescope is the world’s largest, fully-steerable telescope. The GBT’s dish is 100-meters by 110-meters in size, covering 2.3 acres of space. Credit: NRAO/AUI/NSF
Even Wright admits that the “alien hypothesis” should be seen as a last resort. But to make sure no stone goes unturned, Wright, Boyajian and several of the Planet Hunters put together a proposal to do a radio-SETI search with the Green Bank 100-meter telescope. In my opinion, this is science at its best. We have a difficult question to answer, so let’s use all the tools at our disposal to seek an answer.
KIC 8462852, photographed on Oct. 15, 2015. It’s an F3 V star (yellow-white dwarf) located about 1,480 light years from Earth. Credit: Gianluca Masi
In the end, it’s probably not an alien megastructure, just like the first pulsar signals weren’t sent by LGM-1 (Little Green Men). But whatever’s causing the dips, Boyajian wants astronomers to keep a close watch on KIC 8462852 to find out if and when its erratic light variations repeat. I love a mystery, but answers are even better.
Itching for some cometary action? After a fine winter’s performance from Comet C/2014 Q2 Lovejoy, 2015 has seen a dearth of good northern hemisphere comets. That’s about to change, however, as Comet C/2013 US10 Catalina joins the planetary lineup currently gracing the dawn sky in early November. Currently located in the constellation Centaurus and shining at magnitude +6, Comet US10 Catalina has already put on a fine show for southern hemisphere observers over the last few months during Act I.
Currently buried in the dusk sky, Comet US10 Catalina is bashful right now, as it shares nearly the same right ascension with the Sun over the next few weeks, passing just eight degrees from our nearest star as seen from our Earthly vantage point on November 7th — and perhaps passing juuusst inside of the field of view for SOHO’s LASCO C3 camera — and into the dawn sky.
The altitude of Comet US10 Catalina in November and December at dawn as seen from latitude 30 degrees north. Image credit: Starry Night Education software.
The hunt is on come early November, as Comet US 10 Catalina vaults into the dawn sky. From 30 degrees north latitude here in Central Florida, the comet breaks 10 degrees elevation an hour prior to local sunrise right around November 20th. This should see the comet peaking in brightness right around magnitude +5 near perihelion the same week on November 16th.
The projected light curve of Comet US10 Catalina, with observations thus far (black dots) Image credit: Adapted from Seiichi Yoshida’s Weekly Information About Bright Comets
The angle of the comet’s orbit is favorable for northern hemisphere viewers in mid-November, as viewers start getting good looks in the early morning from latitude 30 degrees northward and the comet gains about a degree of elevation per day. This will bring it up out of the murk of twilight and into binocular view.
Mark your calendar for the morning of December 7th, as the crescent Moon, Venus and a (hopefully!) +5 magnitude comet US10 Catalina will all fit within a five degree circle.
The view on the morning of December 7th. Image credit: Starry Night Education software
Here are some key dates with celestial destiny for Comet US10 Catalina for the remainder of 2015:
October
20-Crosses into the constellation Hydra.
November
2-Crosses into the constellation Libra.
16-Crosses into the constellation Virgo.
16-Reaches perihelion at 0.823 AU (127.6 million kilometers) from Sun.
26-Crosses the ecliptic plane northward.
27-Passes less than one degree from the +4.5 magnitude star Lambda Virginis.
The celestial path of Comet US 10 Catalina through the end of 2015. Image Credit: Starry Night Education software
December
7-Fits inside a five degree circle with Venus and the waning crescent Moon.
8-Passes less than one degree from the +4 magnitude star Syrma (Iota Virginis).
17-Crosses the celestial equator northward.
24-Crosses into the constellation Boötes.
In January, Comet US10 Catalina starts the New Year passing less than a degree from the -0.05 magnitude star Arcturus. From there, the comet may drop below +6 magnitude and naked eye visibility by mid-month, just prior to its closest approach to the Earth at 0.725 AU (112.3 million kilometers) on January 17th. By February 1st, the comet may drop below +10th magnitude and binocular visibility, into the sole visual domain of large light bucket telescopes under dark skies.
Comet US10 Catalina imaged from Australia on July 21st, 2015. Image credit: Alan Tough
Or not. Comets and predictions of comet brightness are always notoriously fickle, and rely mainly on just how the comet performs near perihelion. Then there’s twilight extinction to contend with, and the fact that the precious magnitude of the comet is diffused over its extended surface area, often causing the comet to appear fainter visually than the quoted magnitude.
But do not despair. Comets frequently under-perform pre-perihelion passage, only to put on brilliant shows after. Astronomers discovered Comet US10 Catalina on Halloween 2013 from the Catalina Sky Survey based just outside of Tucson, Arizona. On a several million year orbit, all indications are that Comet US10 Catalina is a dynamically new Oort Cloud visitor and will probably get ejected from the solar system after this all-too brief fling with the Sun. Its max velocity at perihelion will be 46.4 kilometers per second, three times faster than the New Horizons spacecraft currently on an escape trajectory out of the solar system.
The odd ‘US10’ designation comes from the comet’s initial identification as an asteroidal object, later upgraded to cometary status. The comet’s high orbital inclination of 149 degrees assured two separate showings, as the comet approached the Sun as seen from the Earth’s southern hemisphere, only to then vault up over the northern hemisphere post-perihelion. As is often the case, the comet was closest to the Sun at exactly the wrong time: had perihelion occurred around May, the comet would’ve passed the Earth just 0.17 AU (15.8 million miles or 26.3 million kilometers) distant! That might’ve placed the comet in the negative magnitudes and perhaps earned it the title of ‘the Great Comet of 2015…’
The orbit of Comet US10 Catalina and the view during closest Earth approach. Image credit: NASA/JPL
But such was not to be.
Ah, but the next ‘big one’ could come at any time. In 2016, we’re tracking comet C/2013 X1 PanSTARRS, which will ‘perhaps’ become a fine binocular comet next summer…
More to come. Perhaps we’ll draft up an Act III for US10 Catalina in early January if it’s a top performer.
Observational astronomy is a study in patience. Since the introduction of the telescope over four centuries ago, steely-eyed observers have watched the skies for star-like or fuzzy points of light that appear to move. Astronomers of yore discovered asteroids, comets and even the occasional planet this way. Today, swiftly moving satellites have joined the fray. Still other ‘new stars’ turn out to be variables or novae.
Tombaugh’s mechanical ‘steampunk starblinker’ on display at the Lowell observatory. Image credit: Dave Dickinson
The advent of photography in the late 19th century upped the game… you’ll recall that Clyde Tombaugh used a blink comparator to discover Pluto from the Lowell Observatory in 1930. Clyde’s mechanical shutter device looked at glass plates in quick sequence. Starblinker takes this idea a step further, allowing astro-imagers to compare two images in rapid sequence in a similar ‘blink comparator’ fashion. You can even quickly compare an image against one online from, say, the SDSS catalog or Wikipedia or an old archival image. Starblinker even automatically orients and aligns the image for you. Heck, this would’ve been handy during a certain Virtual Star Party early last year hosted by Universe Today, making the tale of the ‘supernova in M82 that got away’ turn out very differently…
Often times, a great new program arises simply because astrophotographers find a need where no commercial offering exists. K3CCD Tools, Registax, Orbitron and Deep Sky Stacker are all great examples of DIY programs that filled a critical astronomy need which skilled users built themselves.
“I started to code the software after the mid of last month,” Starblinker creator Marco Lorrai told Universe Today. “I knew there was a plugin for MaximDL to do this job, but nothing for people like me that make photos just with a DSLR… I own a 250mm telescope, and my images go easily down to magnitude +18 so it is not impossible to find something interesting…”
Starblinker is a free application, and features a simple interface. Advanced observers have designed other programs to sift through video and stacks of images in the past, but we have yet to see one with such a straight-forward user interface with an eye toward quick and simple use in the field.
Starblinker screenshot. Image credit: Marco Lorrai
“The idea came to me taking my astrophotos: many images are so rich with stars, why not analyze (them) to check if something has changed?” Lorrai said. “I started to do this check manually, but the task was very thorny, because of differences in scale and rotation between the two images. Also, the ‘blinking’ was done loading two alternating windows containing two different images… not the best! This task could be simplified if someone already has a large set of images for comparison with one old image (taken) with the same instrument… a better method is needed to do this check, and then I started to code Starblinker.”
Why Starblinker
I can see a few immediate applications for Starblinker: possible capture of comets, asteroids, and novae or extragalactic supernovae, to name a few. You can also note the variability of stars in subsequent images. Take images over the span of years, and you might even be able to tease out the proper motion of nearby fast movers such as 61 Cygni, Kapteyn’s or even Barnard’s Star, or the orbits of double stars. Or how about capturing lunar impacts on the dark limb of the Moon? It may sound strange, but it has been done before… and hey, there’s a lunar eclipse coming right up on the night of September 27/28th. Just be careful to watch for cosmic ray hits, hot pixels, satellite and meteor photobombs, all of which can foil a true discovery.
The Dumbell Nebula (M27). Note the (possible) variable star (marked). Image credit: Marco Lorrai
“A nice feature to add could be the support for FITS images and I think it could be very nice that… the program could retrieve automatically a comparison image, to help amateurs that are just starting (DSLR imaging).” Lorrai said.
And here is our challenge to you, the skilled observing public. What can YOU do with Starblinker? Surprise us… as is often the case with any hot new tech, ya just never know what weird and wonderful things folks will do with it once it’s released in the wild. Hey, discover a comet, and you could be immortalized with a celestial namesake… we promise that any future ‘Comet Dickinson’ will not be an extinction level event, just a good show…
Think you’ve discovered a comet? Nova? A new asteroid? Inbound alien invasion fleet? OK, that last one might be tweet worthy, otherwise, here’s a handy list of sites to get you started, with the checklist of protocols to report a discovery used by the pros:
A fine sungrazer nears its doom as seen via SOHOs LASCO C2 camera. Image credit: NASA/ESA/SOHO/NRLSungrazers
It’s a discovery that could come any day now.
The Solar Heliospheric Observatory spacecraft known as SOHO is set to cross the 3,000 comet discovery threshold this month. Launched atop an Atlas II rocket on December 2nd, 1995, SOHO is a joint NASA/ESA mission, and has observed the Sun now for almost 20 years from the sunward L1 lagrange point. That fact is amazing enough, as SOHO has already followed the goings on of our tempestuous host star for nearly two full solar cycles.
And though SOHO wasn’t initially designed as a comet hunter extraordinaire, it has gone on to discover far more comets than anyone—human or robotic.
SOHO on Earth. Image credit: NASA/ESA/SOHO
The U.S. Naval Research Laboratory’s (NRL) sungrazer website lists the discovery count as 2,987 as of July 31, 2015, with more comets awaiting verification daily. “In the past, SOHO has often discovered as many as four or five comets in a single day,” Karl Battams, a solar scientist at the NRL told Universe Today. “Suffice to say, it really could be any day now, given how close we are to 3,000! I actually expected it to be a month ago, so I’m surprised it’s dragging out like this. Predicting comets is fraught with uncertainty!”
Part of what gives SOHO an edge is its LASCO (the Large Angle and Spectrometric Coronagraph) C2 and C3 coronagraphs. With a field of view about 15 degrees wide, the C3 imager monitors the faint corona of the Sun, while blocking its dazzling disk. The corona is the pearly white outer atmosphere of the Sun, and is about half as bright as a Full Moon. On Earth, we only see the corona briefly during a total solar eclipse. SOHO routinely sees sungrazing comets ‘photobomb’ the view of its LASCO C3 camera, sometimes to the tune of more than 200 a year.
Comet NEAT makes its way through the field of view of SOHO’s LASCO C2 camera in 2003. Image credit: NASA/ESA/NRL/Sungrazers
SOHO has rewritten the history of sungrazers. How far we’ve come: flashback to 1979, and less than a dozen sungrazers were known, one being the famous Comet Ikeya-Seki in 1965. Early space-based platforms such as Solwind and SMM sported early coronagraphs, and paved the way for SOHO. Think about that for a moment; a vast majority of the cometary population of the solar system was simply sliding by, unobserved from the ground. And this was only a generation ago.
Most of what SOHO sees are what’s termed as Kreutz group sungrazers. First theorized by astronomer Heinrich Kreutz in 1888, SOHO has given researchers the ability to classify and characterize the orbits of these doomed comets. These sungrazers nearly always incinerate during their perihelion passage. C/2011 W3 Lovejoy was a famous exception, which passed about 140,000 kilometers from the surface of the Sun on December 16th, 2011 and went on to become a fine southern hemisphere comet.
“We knew little of the Kreutz population, other than that it seemed there were ‘a few’ objects on the Kreutz path,” Battams said. “I would say that probably when the Sungrazer Project was launched in late 2000 was the point at which the team realized that this was something more than just seeing an occasional comet.”
The typical track of a Kreutz-group comet. Click here for the full diagram of C2/C3 tracks throughout the year. Image Credit: NASA/ESA/SOHO
Kreutz comets also have seasons and predictable directions of approach along the ecliptic as seen from SOHO’s point of view. Some periodic comets, such as 96P Machholz, — which orbits the Sun once every six years — have become old friends. To date, SOHO has observed 96P Machholz four times.
Upping the Comet Hunting Game
But here’s the amazing second half of the tale. Legions of dedicated amateurs make these discoveries, patiently combing over daily images sent back by SOHO. In many ways, SOHO has grown up with the rise of the internet. Think about it: what was your internet surfing experience like way back in 1995? Karl Battams at NRL relays these discoveries to the Central Bureau for Astronomical Telegrams, the clearing house for potential comet discoveries. Founded in 1882 and based at Harvard College Observatory since 1965, CBAT actually received its last ‘telegram’ announcing the possible discovery that would become Comet Hale-Bopp in 1995.
The rise of automated surveys and satellites such as SOHO has definitely upped the game. To date, the all-time human champ amongst comet hunters is Robert H. McNaught, with the discovery of 44 long-period and 26 short-period comets.
And I think we can all remember where we were on U.S. Thanksgiving Day 2013, as SOHO gave us a front row seat to the demise of Comet ISON. It’s been a roller coaster ride for sure, and it’s hard to imagine a time now when we didn’t have SOHO as a daily resource. Heck, it’s just fun to watch planets transit the field of view of SOHO, as they move from the dawn to dusk sky and back again.
Looking at the “SOHO Bump” and the rise of automated comet hunters in the early 21st century. Image credit: Dave Dickinson
Comet hunting via SOHO is fun and easy to do, though yes, there are lots of eyeballs out there looking, so you have some pretty dedicated competition. Patience is key, and there’s also a dedicated message board describing the latest discoveries and known objects entering the field of view that have already been identified.
“What’s the future of SOHO? “December is SOHO’s 20th anniversary, so that’s another milestone,” Battams said. “Beyond that, who knows? Engineers designed SOHO to operate for two years, and with no intention of comet discovery; it has lasted 20 years and re-written the history books for comets. It remains the only coronagraph we have along the Sun-Earth line, so for space weather forecasting it remains a unique and valuable asset.”
Congrats, and be sure to follow Karl Battam’s @SungrazerComets account on Twitter… number 3,000 could be discovered any day now!
This sequence of images, taken with Rosetta's OSIRIS narrow-angle camera on 30 July 2015, show a boulder-sized object close to the nucleus of Comet 67P/Churyumov-Gerasimenko.
The images were captured on 30 July 2015, about 185 km from the comet. The object measures between one and 50 m across; however, the exact size cannot be determined as it depends on its distance to the spacecraft, which cannot be inferred from these images. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
How would you like to see one of the most famous comets with your own eyes? Comet 67P/Churyumov-Gerasimenko plies the morning sky, a little blot of fuzzy light toting an amazing visitor along for the ride — the Rosetta spacecraft. When you look at the coma and realize a human-made machine is buzzing around inside, it seems unbelievable.
Comet 67P/Churyumov-Gerasimenko plows through a rich star field in Gemini on the morning of August 20, 2015. Photos show a short, faint tail to the west not visible to the eye in most amateur telescopes. Credit: Efrain Morales
If you have a 10-inch or larger telescope, or you’re an experienced amateur with an 8-inch and pristine skies, 67P is within your grasp. The comet glows right around magnitude +12, about as bright as it will get this apparition. Periodic comets generally appear brightest around and shortly after perihelion or closest approach to the Sun, which for 67P/C-G occurred back on August 13.
The surface of Comet 67P/C-G is extensively fractured due to loss of volatile ices, the expansion and contraction of the comet from solar heating and bitter cold and possibly even tectonic forces. The smaller polygonal shapes outlined by fractures in the lower right photo are just 6-16 feet (2-5 meters) across. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
You’ll be looking for a small, 1-arc-minute-diameter, compact, circular patch of nebulous light shortly before dawn when it’s highest in the east. Rosetta’s Comet will spend the remainder of August slicing across Gemini the Twins north of an nearly parallel to the ecliptic. I spotted 67P/C-G for the first time this go-round about a week ago in my 15-inch (37 cm) reflector. While it appears like a typical faint comet, thanks to Rosetta, we know this particular rough and tumble mountain of ice better than any previous comet. Photographs show rugged cliffs, numerous cracks due to the expansion and contraction of ice, blowholes that serve as sources for jets and smooth plains blanketed in fallen dust.
Geysers of dust and gas shooting off the comet’s nucleus are called jets. The material they deliver outside the nucleus builds the comet’s coma. Credit: ESA/Rostta/NAVCAM
The jets are geyser-like sprays of dust and gas that loft grit and rocks from the comet’s interior and surface into space to create a coma or temporary atmosphere. This is what you’ll see in your telescope. And if you’re patient, you’ll even be able to catch this glowing tadpole on the move. I was surprised at its speed. After just 20 minutes, thanks to numerous field stars that acted as references, I could easily spot the comet’s eastward movement using a magnification of 245x.
Facing east around 4 a.m. local time in late August, you’ll see the winter constellations Gemini and Orion. 67P/C-G’s path is shown through early September. Brighter stars near the path are labeled. Time shown is 4 a.m. CDT. Use this map to get oriented and then switch to the one below for telescope use. Source: Chris Marriott’s SkyMap
Tomorrow morning, 67P/C-G passes very close to the magnitude +5 star Omega Geminorum. While this will make it easy to locate, the glare may swamp the comet. Set your alarm for an hour before dawn’s start to allow time to set up a telescope, dark-adapt your eyes and track down the field where the comet will be that morning using low magnification.
Once you’ve centered 67P/C-G’s position, increase the power to around 100x-150x and use averted vision to look for a soft, fuzzy patch of light. If you see nothing, take it to the next level (around 200-250x) and carefully search the area. The higher the magnification, the darker the field of view and easier it will be to spot it.
Detailed map showing the comet’s path through central Gemini daily August 21-28, 2015 around 4 a.m. CDT. Brighter stars are marked with Greek letters and numbers. “57”= 57 Geminorum. North is up, east to the left and stars to magnitude +13.5. Click for a larger version you can print out. Source: Chris Marriott’s SkyMap
Besides being relatively faint, the comet doesn’t get very high in the east before the onset of twilight. Low altitude means the atmosphere absorbs a share of the comet’s light, making it appear even fainter. Not that I want to dissuade you from looking! There’s nothing like seeing real 67P photons not to mention the adventure and sense of accomplishment that come from finding the object on your own.
As we advance into late summer and early fall, 67P/C-G will appear higher up but also be fading. Now through about August 27 and again from September 10-24 will be your best viewing times. That’s when the Moon’s absent from the sky.
Given the comet’s current distance from Earth of 165 million miles and apparent visual size of just shy of 1 arc minute, the coma measures very approximately 30,000 miles across. Rosetta orbits the comet’s 2.5-mile-long icy nucleus at a distance of about 115 miles (186 km), meaning it’s snug up against the nuclear center from our point of view on the ground.
Halleys Comet, as seen in May 1986. Credit and copyright: Bob King.
The idea of panspermia — that life on Earth originated from comets or asteroids bombarding our planet — is not new. But new research may have given the theory a boost. Scientists from Japan say their experiments show that early comet impacts could have caused amino acids to change into peptides, becoming the first building blocks of life. Not only would this help explain the genesis of life on Earth, but it could also have implications for life on other worlds.
Dr. Haruna Sugahara, from the Japan Agency for Marine-Earth Science and Technology in Yokahama, and Dr. Koichi Mimura, from Nagoya University said they conducted “shock experiments on frozen mixtures of amino acid, water ice and silicate (forsterite) at cryogenic condition (77 K),” according to their paper. “In the experiments, the frozen amino acid mixture was sealed into a capsule … a vertical propellant gun was used to [simulate] impact shock.”
They analyzed the post-impact mixture with gas chromatography, and found that some of the amino acids had joined into short peptides of up to 3 units long (tripeptides).
Based on the experimental data, the researchers were able to estimate that the amount of peptides produced would be around the same as had been thought to be produced by normal terrestrial processes (such as lighting storms or hydration and dehydration cycles).
Artists concept of the stardust spacecraft flying throug the gas and dust from comet Wild 2. Credit: NASA/JPL“This finding indicates that comet impacts almost certainly played an important role in delivering the seeds of life to the early Earth,” said Sugahara. “It also opens the likelihood that we will have seen similar chemical evolution in other extraterrestrial bodies, starting with cometary-derived peptides.”
The earliest known fossils on Earth are from about 3.5 billion years ago and there is evidence that biological activity took place even earlier. But there’s evidence that early Earth had little water and carbon-based molecules on the Earth’s surface, so how could these building blocks of life delivered to the Earth’s surface so quickly? This was also about the time of the Late Heavy Bombardment, and so the obvious answer could be the collision of comets and asteroids with the Earth, since these objects contain abundant supplies of both water and carbon-based molecules.
A view of NASA’s Deep Impact probe colliding with comet Tempel 1, captured by the Deep Impact flyby spacecraft’s high-resolution instrument.
Space missions to comets are helping to confirm this possibility. The 2004 Stardust mission found the amino acid when it collected particles from Comet Wild 2. When NASA’s Deep Impact spacecraft crashed into Comet Tempel 1 in 2005, it discovered a mixture of organic and clay particles inside the comet. One theory about the origins of life is that clay particles act as a catalyst, allowing simple organic molecules to get arranged into more and more complex structures.
The news from the current Rosetta mission to comet 67P/Churyumov-Gerasimenko also indicates that comets are a rich source of materials, and more discoveries are likely to be forthcoming from that mission.
Jets of gas and dust are blasting from the active neck of comet 67P/Churyumov-Gerasimenko in this photo mosaic assembled from four images taken on 26 September 2014 by the European Space Agency’s Rosetta spacecraft at a distance of 26.3 kilometers (16 miles) from the center of the comet. Credit: ESA/Rosetta/NAVCAM/Marco Di Lorenzo/Ken Kremer/kenkremer.com
“Two key parts to this story are how complex molecules are initially generated on comets and then how they survive/evolve when the comet hits a planet like the Earth,” said Professor Mark Burchell from the University of Kent in the UK, commenting on the new research from Japan. “Both of these steps can involve shocks which deliver energy to the icy body… building on earlier work, Dr. Sugahara and Dr. Mimura have shown how amino acids on icy bodies can be turned into short peptide sequences, another key step along the path to life.”
“Comet impacts are normally associated with mass extinction on Earth, but this works shows that they probably helped kick-start the whole process of life in the first place,” said Sugahara. “The production of short peptides is the key step in the chemical evolution of complex molecules. Once the process is kick-started, then much less energy is needed to make longer chain peptides in a terrestrial, aquatic environment.”
The scientists also indicated that similar “kickstarting” could have happened in other places in our Solar System, such as on the icy moons Europa and Enceladus, as they likely underwent a similar comet bombardment.
Sequence of OSIRIS narrow-angle camera images from 12 August 2015, just a few hours before the comet reached perihelion. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Sequence of OSIRIS narrow-angle camera images from 12 August 2015, just a few hours before the comet reached perihelion. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
See hi res images below[/caption]
A spectacular display of celestial fireworks like none ever witnessed before, burst forth from Rosetta’s comet right on time – commemorating the Europeans spacecraft’s history making perihelion passage after a year long wait of mounting excitement and breathtaking science.
As the European Space Agency’s (ESA’s) Rosetta marked its closest approach to the Sun (perihelion) at exactly 02:03 GMT on Thursday, August 13, 2015, while orbiting Comet 67P/Churyumov–Gerasimenko, its suite of 11 state-of-the-art science instruments, cameras and spectrometers were trained on the utterly bizarre bi-lobed body to capture every facet of the comet’s nature and environment for analysis by the gushing science teams.
And the perihelion passage did not disappoint – living up to its advance billing by spewing forth an unmatched display of otherworldly outbursts of gas jets and dust particles due to surface heating from the warming effects of the sun as the comet edged ever closer, coming within 186 million kilometers of mighty Sol.
ESA has released a brand new series of images, shown above and below, documenting sparks flying – as seen by Rosetta’s OSIRIS narrow-angle camera and NAVCAM wider angle cameras on August 12 and 13 – just a few hours before the rubby ducky shaped comet reached perihelion along its 6.5-year orbit around the sun.
Images of Comet 67P/C-G taken with OSIRIS narrow-angle camera on 12 August 2015, just a few hours before the comet reached perihelion, about 330 km from the comet. The individual images are also available below. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Indeed the navcam camera image below was taken just an hour before the moment of perihelion, at 01:04 GMT, from a distance of around 327 kilometers!
Frozen ices are seen blasting away from the comet in a hail of gas and dust particles as rising solar radiation heats the nucleus and fortifies the comet’s atmosphere, or coma, and its tail.
Comet at perihelion. Single frame Rosetta navigation camera image acquired at 01:04 GMT on 13 August 2015, just one hour before Comet 67P/Churyumov–Gerasimenko reached perihelion – the closest point to the Sun along its 6.5-year orbit. The image was taken around 327 km from the comet. It has a resolution of 28 m/pixel, measures 28.6 km across and was processed to bring out the details of the comet’s activity. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
After a decade long chase of over 6.4 billion kilometers (4 Billion miles), ESA’s Rosetta spacecraft arrived at the pockmarked Comet 67P/Churyumov-Gerasimenko exactly a year ago on Aug. 6, 2014 for history’s first ever attempt to orbit a comet for long term study.
In the interim, Rosetta also deployed the piggybacked Philae lander for history’s first landing on a comet on Nov. 12, 2014.
In fact, measurements from Rosetta’s science instruments confirm the comet is belching a thousand times more water vapor today than was observed during Rosetta’s arrival a year ago. It’s spewing some 300 kg of water vapour every second now, compared to just 300 g per second upon arrival. That equates to two bathtubs per second now in Aug. 2015 vs. two small glasses of water per second in Aug. 2014.
Besides gas, 1000 kg of dust per second is simultaneously erupting from the nucleus, “creating dangerous working conditions for Rosetta,” says ESA.
“In recent days, we have been forced to move even further away from the comet. We’re currently at a distance of between 325 km and 340 km this week, in a region where Rosetta’s startrackers can operate without being confused by excessive dust levels – without them working properly, Rosetta can’t position itself in space,” comments Sylvain Lodiot, ESA’s spacecraft operations manager, in an ESA statement.
Here’s an OSIRIS image taken just hours prior to perihelion, that’s included in the lead animation of this story.
OSIRIS NAC image of Comet 67P/C-G taken on 12 August 2015 at 17:35 GMT. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
The period of the comet’s peak intensity, as seen in all these images, is expected to continue past perihelion for several weeks at least and fulfils the dreams of a scientific goldmine for all the research teams and hundreds of researchers involved with Rosetta and Philae.
“Activity will remain high like this for many weeks, and we’re certainly looking forward to seeing how many more jets and outburst events we catch in the act, as we have already witnessed in the last few weeks,” says Nicolas Altobelli, acting Rosetta project scientist.
And Rosetta still has lots of fuel, and just as important – funding – to plus up its ground breaking science discoveries.
ESA recently granted Rosetta a 9 month mission extension to continue its research activities as well as having been given the chance to accomplish one final and daring historic challenge.
Engineers will attempt to boldly go and land the probe on the undulating surface of the comet.
Officials with the European Space Agency (ESA) gave the “GO” on June 23 saying “The adventure continues” for Rosetta to march forward with mission operations until the end of September 2016.
If all continues to go well “the spacecraft will most likely be landed on the surface of Comet 67P/Churyumov-Gerasimenko” said ESA.
ESA Philae lander approaches comet 67P/Churyumov–Gerasimenko on 12 November 2014 as imaged from Rosetta orbiter after deployment and during seven hour long approach for 1st ever touchdown on a comets surface. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA – Composition by Marco Di Lorenzo/Ken Kremer
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.
Jets of gas and dust are blasting from the active neck of comet 67P/Churyumov-Gerasimenko in this photo mosaic assembled from four images taken on 26 September 2014 by the European Space Agency’s Rosetta spacecraft at a distance of 26.3 kilometers (16 miles) from the center of the comet. Credit: ESA/Rosetta/NAVCAM/Marco Di Lorenzo/Ken Kremer/kenkremer.com
Rosetta’s scientific camera OSIRIS show the sudden onset of a well-defined jet-like feature emerging from the side of the comet’s neck, in the Anuket region. Image Credit: ESA/Rosetta/OSIRIS
A comet on a comet? That’s what it looks like, but you’re witnessing the most dramatic outburst ever recorded at 67P/Churyumov-Gerasimenko by the Rosetta spacecraft. The brilliant plume of gas and dust erupted on July 29 just two weeks before perihelion.
In a remarkable display of how quickly conditions on a comet can change, the outburst lasted only about 18 minutes, but its effects reverberated for days.
In this sequence of images, the one at left was taken at 8:06 a.m. CDT and doesn’t show any visible signs of the jet. 18 minutes later at 8:24, it’s very bright and distinct (middle image) with only residual traces of activity remaining in the final photo made at 8:42. The photos were taken from a distance of 116 miles (186 km) from the center of the comet. Copyright: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
In a sequence of images taken by Rosetta’s scientific camera OSIRIS, the brilliant, well-defined jet erupts from the side of the comet’s neck in the Anuket region. It was first seen in a photo taken at 8:24 a.m. CDT, but not in one taken 18 minutes earlier, and had faded significantly in an image captured 18 minutes later. The camera team estimates the material in the jet was traveling at a minimum of 22 mph (10 meters/sec), but possibly much faster.
It’s the brightest jet ever seen by Rosetta. Normally, the camera has to be set to overexpose 67P/C-G’s nucleus to reveal the typically faint, wispy jets. Not this one. You can truly appreciate its brilliance because a single exposure captures both nucleus and plume with equal detail.
Jets are normally faint and require special processing or longer exposures to bring out in photos., overexposing the nucleus in the process. Comet 67P/Churyumov-Gerasimenko photographed from about 125 miles away on June 5 Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
We all expected fireworks as the comet approached perihelion in its 6.5 year orbit around the Sun. Comets are brightest at and shortly after perihelion, when they literally “feel the heat”. Solar radiation vaporizes both exposed surface ices and ice locked beneath the comet’s coal-black crust. Vaporizing subsurface ice can created pressurized pockets of gas that seek a way out either through an existing vent or hole or by breaking through the porous crust and erupting geyser-like into space.
Jets carry along dust that helps create a comet’s fuzzy coma or temporary atmosphere, which are further modified into tails by the solar wind and the pressure of sunlight. When conditions and circumstances are right, these physical processes can build comets, the sight of which can fill the human heart with both terror and wonder.
The decrease in magnetic field strength measured by Rosetta’s RPC-MAG instrument during the outburst event on July 29, 2015. This is the first time a ‘diamagnetic cavity’ has been detected at Comet 67P/Churyumov–Gerasimenko and is thought to be caused by an outburst of gas temporarily increasing the gas flux in the comet’s coma, and pushing the pressure-balance boundary between it and incoming solar wind farther from the nucleus than expected under ‘normal’ levels of activity. Credit: ESA/Rosetta/RPC/IGEP/IC
This recent show of activity may be just the start of a round of outbursts at 67P/C-G. While perihelion occurs on this Thursday, a boost in a comet’s activity and brightness often occurs shortly after, similar to the way the hottest part of summer lags behind the date of summer solstice.
Rosetta found that the brief and powerful jet did more than make a spectacle — it also pushed away the solar wind’s magnetic field from around the nucleus as observed by the ship’s magnetometer. Normally, the Sun’s wind is slowed to a standstill when it encounters the gas cloud surrounding the nucleus.
“The solar wind magnetic field starts to pile up, like a traffic jam, and eventually stops moving towards the comet nucleus, creating a magnetic field-free region on the Sun-facing side of the comet called a ‘diamagnetic cavity’,” explained Charlotte Götz, magnetometer team member, on the ESA Rosetta website.
The red circle shows the location of the July 29, 2015 outburst on 67P/C-G. Copyright: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Only once before at Halley’s Comet has a magnetically “empty” region like this been observed. But that comet was so much more active than 67P/C-G and up until July 29, Halley’s remained the sole example. But following the outburst on that day, the magnetometer detected a diamagnetic cavity extending out at least 116 miles (186 km) from the nucleus. This was likely created by the outburst of gas, forcing the solar wind to ‘stop’ further away from the comet and thus pushing the cavity boundary outwards beyond where Rosetta was flying at the time.
Pew! The graph shows the relative abundances of various gases after the outburst, compared with the measurements two days earlier. Water remained the same, but CO2 and especially increased dramatically. Copyright: ESA/Rosetta/ROSINA/UBern/ BIRA/LATMOS/LMM/IRAP/MPS/SwRI/TUB/UMich
Soon afterward the outburst, the comet pressure sensor of ROSINA detected changes in the structure of the coma, while its mass spectrometer recorded changes in the composition of outpouring gases. Compared to measurements made two days earlier, carbon dioxide increased by a factor of two, methane by four, and hydrogen sulphide by seven, while the amount of water stayed almost constant. No question about it – with all that hydrogen sulfide (rotten egg smell), the comet stunk! Briefly anyway.
It was also more hazardous. In early July, Rosetta recorded and average of 1-3 dust hits a day, but 14 hours after the event, the number leapt to 30 with a peak of 70 hits in one 4-hour period on August 1. Average speeds picked up, too, increasing from 18 mph (8 m/s) to about 45 mph (20 m/s), with peaks at 67 mph (30 m/s). Ouch!
“It was quite a dust party!” said Alessandra Rotundi, principal investigator of GIADA (Grain Impact Analyzer and Dust Accumulator).
67P/C-G’s little party apparently wasn’t enough to jack up its brightness significantly as seen from Earth, but that doesn’t mean future outbursts won’t. We’ll be keeping an eye on any suspicious activity through perihelion and beyond and report back here.
