The Coming of Comet C/2019 Y4 ATLAS

One of the great things about staying at home - you just, might discover a comet! Ninety-four (94) new comets were discovered by Amateur Astronomers last year.

The last great comet that I saw was Comet Hale-Bopp in 1997. When I say, "Great" - I mean that it was so prominent in the sky that, if you were facing about 70-80 degrees away from it, it still caught your attention out of the corner of your eye. Now, THAT's "Great"!

Another comet that I've always considered to be "Great" was comet Hyakutake (C/1996 B2). Most people don't remember that one - but that's only because it was so large that it was difficult to see as a singular, intact object. The tail of the comet was so wide and was positioned directly overhead that it looked more like a disintegrating, diffuse airliner contrail - spanning nearly the entire sky, and with no distinct "head".

Comet C/2019 Y4 ATLAS imaged on the 16" f/3.75 Dream Aerospace Systems astrograph reflector, ATEO-1 on the evening of April 10, 2020, by Muir Evenden. Processing by Utkarsh Mishra and Michael Petrasko.

But enough about those "Great visitors" to the Inner Solar System - there just might be another, looming presence in the night. Enter comet C/2019 Y4 ATLAS, or, comet "ATLAS", for short!) ATLAS is a sort of "Rip Van Winkle"; it's been "asleep" since about the year 3000 BC! The chart here shows the comet's expected positions in the sky, from 20MAR, in Ursa Major, to 28JUN, 2020 in Orion. Currently, it is "cat-napping", in the northern constellation Camelopardalis. On 12MAY, the comet moves into the constellation Perseus, and on the 23rd, it will be at its closest to Earth. It will be at its closest to the Sun on 31 May 2000.

The dirty "snow-ball" - as we like to call these things - was discovered by one of the Asteroid Terrestrial-Impact Last Alert System's (ATLAS) 0.5 m (20 in) reflector telescopes, situated at the top of Mauna Loa, Hawaii. At the time of discovery, in December of 2019, it was 3 AU from the Sun, at magnitude 19.6. By the beginning of February, it brightened to magnitude 17, and then, to mag. 8, by the end of March of this year.

The predicted path of Comet C/2019 Y4 ATLAS through June 18th, 2020. Graphic credit: www.cometwatch.co.uk

ATLAS has a very distinctive coloration; green/aqua, due to diatomic carbon molecules within its coma. Its orbital period was originally thought to be around 4,400 years. ATLAS has some orbital characteristic similarities with the Great Comet of 1844 (C/1844 Y1), suggesting that this "new" (to us) comet might, actually, be a remnant fragment of the same parent body as C/1844 Y1. This apparition of ATLAS was, initially, held to be possibly a spectacular one - and that may still be the case. However, recent observations have shown a decrease in magnitude, after having brightened to magnitude 8, as it crossed the orbit of Mars. It is currently at magnitude 8.9 - 9.2. This is not even naked-eye or unaided-eye visibility. That's because the comet is fragmenting. It is still possible that the fragments will maintain enough structural integrity to give the broken comet higher scores - possibly something along the lines of comet Shoemaker-Levy's plunge into the atmosphere of Jupiter, years ago! (We couldn't see that from the ground, but it was spectacular on a spacecraft video feed!).

Well, who knows?! When ATLAS is done doing what it's going to do, it will head back out into the cosmic depths, on a 5,200-year-long loop, eventually, bringing it back around to the sun, once again. Along the way, it may even leave behind a generous portion of its disintegrating self in the form of a new meteor shower stream!

Dale Alan Bryant
Senior Contributing Science Writer

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Comet Hunters

Main-belt comets are a recently discovered population of small bodies residing in the Solar System's asteroid belt, exhibiting distinctive tails that we typically associate with comets. Very little is known about main-belt comets, as only about 10 have been discovered to date, but with a larger sample, we could probe the origins of the Solar System and the active processes occurring in today's asteroid belt.

View of Mauna Kea (one of the best astronomical observing sites in the world) from the Subaru Telescope Cat Walk - Image Credit: M. E. Schwamb.

Zooniverse.org has initiated the Comet Hunters project to try to greatly increase the discovery rate of these objects. Some main-belt comets were first known as inactive main-belt asteroids and then were only found to have cometary activity in later observations. Asteroids frequently appear by chance in wide-field astronomical observations, and so by scanning through these images, we may have a chance of finding more active objects. We have extracted images of known main-belt asteroids from the public archives of the Subaru Telescope, one of the largest telescopes in the world (at 8.2 meters, or 27 feet, across), located on Mauna Kea in Hawaii. None of the objects we are targeting has been previously known to show activity, but most have so far only previously been studied using small telescopes that may have missed faint activity.

Discovery image of a comet-like activity in bright main-belt asteroid Griseldis taken on the Subaru Telescope on Mauna Kea - Image Credit: Adapted from a figure by D. Tholen, S. Sheppard, C. Trujillo - original image.

This is important because we believe we can discover many more main-belt asteroids if we can detect fainter activity, and the way to detect fainter activity is to use larger telescopes like Subaru. Detecting comet-like activity is not easy. Comets can have a wide variety of appearances, and it is difficult to design automated routines to detect all the different types of cometary behavior that might exist in telescope images. In contrast, the human eye can easily spot tails of many different shapes and sizes that indicate cometary activity.

This is where you come in. By reviewing asteroid images on the Comet Hunters website to identify whether the asteroids have a tail or not, you can help find new candidate main-belt comets that the Comet Hunters science team will then follow up with ground- and space-based telescopes. Most of these chance asteroid observations have never been reviewed for cometary activity before. You just might be the first to discover that an asteroid is really a comet!

Zooniverse.org would love to see Comet Hunters incorporated into the classroom:

A wide variety of ages should be able to perform the task we are asking volunteers to do in the main classification interface in order to help identify new comets residing in our Solar System’s asteroid belt.

You might find some resources on NASA's Asteroid and Comet Watch page helpful. If you are interested in building a scale Solar System to show students where the asteroid belt is located, you can find a guide here.

The Comet Hunters Blog is also a great place to keep up with the latest science results and news from the project. Comet Hunters are currently showing images of previously discovered asteroids with well-characterized orbits.

If you develop a lesson based around Comet Hunters, please consider sharing it by uploading it to the Zooniverse Zoo Teach platform. Also, check out the Zooniverse's Education Talk discussion board to interact with the Zooniverse Education Team and other teachers interested in utilizing citizen science in the classroom.

Learn more at https://www.zooniverse.org/projects/mschwamb/comet-hunters/about/research

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Imaging the April Fools Comet

As we have spent most of our time the past few months planning for the big road trip to New Mexico to install the Astronomical Telescope for Educational Outreach (ATEO), I thought it would be nice to do a little remote imaging during one of our weekly ATEO planning conference calls. With all of the comets that have been observable lately, why not quickly capture an image of one remotely from one of iTelescope's remote robotic telescopes, hosted at New Mexico Skies. This remote telescope hosting facility is not too far from where Insight Observatory's ATEO telescope will be hosted just over a month from now at SkyPi Online Observatories.

Comet 41P/Tuttle-Giacobini-Kresák pictured with the star Beta Draconis (lower right).
 Image by Insight Observatory.

On the morning of Thursday, April 20, 2017, at 5:05 am EDT, I logged into iTelescope's T14 which is Takahashi FSQ Fluorite with a Petzval Apochromat Astrograph optical design for taking wide-field images. The CCD camera used to image the comet was an SBIG STL-11000M. The image is a simple combined 2 luminances at 5 minutes a piece. The comet's location was just north of the star Beta Draconis in the constellation Draco. If you zoom into the image, you will notice there are two comet nuclei. This demonstrates how much the comet moved between both five-minute images.

Comet 41P/Tuttle-Giacobini-Kresák, a comet whose identity took nearly 100 years to pin down, made its closest approach to Earth on Saturday, April 1st, just in time for April Fools' Day, but it was not a cosmic prank. It was the comet's closest Earth encounter in more than 50 years, and maybe more than a century stated NASA officials.

The comet was first discovered in 1858 by Horace Parnell Tuttle of the Harvard College Observatory, Cambridge, Massachusetts. It was then re-discovered by Michel Giacobini in 1907 and Ľubor Kresák in 1951. The comet had two close encounters with Jupiter that altered its orbit slightly. A member of the Jupiter family of comets, 41P makes a trip around the sun every 5.4 years, coming relatively close to Earth on some of those trips. On this approach, the comet will pass our planet at a distance of about 13 million miles (0.14 astronomical units), or about 55 times the distance from Earth to the moon.

As the comet passed closest to Earth (0.14 a.u.) from mid-March through early April, it continued to hurry across the circumpolar constellations Ursa Major and Draco. Created with Chris Marriott's SkyMap

"Comet hunters in the Northern Hemisphere should look for it near the constellations Draco and Ursa Major, which the Big Dipper is part of," NASA officials said in a statement. "Whether a comet will put on a good show for observers is notoriously difficult to predict, but 41P has a history of outbursts, and put on quite a display in 1973. If the comet experiences similar outbursts this time, there's a chance it could become bright enough to see with the naked eye. The comet was expected to reach perihelion, or its closest approach to the sun, on April 12." The comet should stay visible through the month of July this year.

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