Artist's impression of Oumuamua leaving the Solar System. Credit: NASA
On October 19th, 2017, the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) in Hawaii announced the first-ever detection of an interstellar object, named 1I/2017 U1 (aka. ‘Oumuamua). In the months that followed, multiple follow-up observations were conducted to learn more about this visitor, as well as resolve the dispute about whether it was a comet and an asteroid.
Rather than resolving the dispute, additional observations only deepened the mystery, even giving rise to suggestions that it might be an extra-terrestrial solar sail. For this reason, scientists are very interested in finding other examples of ‘Oumuamua-like objects. According to a recent study by a team of Harvard astrophysicists, it is possible that interstellar objects enter our system and end up falling into in our Sun somewhat regularly.
Rosetta mission poster showing the deployment of the Philae lander to comet 67P/Churyumov-Gerasimenko.. Credit: ESA/ATG medialab (Rosetta/Philae); ESA/Rosetta/NavCam (comet)
In 2014 , the European Space Agency’s (ESA) Rosetta spacecraft made history when it rendezvoused with Comet 67P/Churyumov-Gerasimenko. This mission would be the first of its kind, where a spacecraft intercepted a comet, followed it as it orbited the Sun, and deployed a lander to its surface. For the next two years, the orbiter would study this comet in the hopes of revealing things about the history of the Solar System.
In this time, Rosetta’s science team also directed the orbiter to look for signs of the comet’s bow shock – the boundary that forms around objects as a result of interaction with solar wind. Contrary to what they thought, a recent study has revealed that Rosetta managed to detect signs of a bow shock around the comet in its early stages. This constitutes the first time in history that the formation of a bow shock has been witnessed in our Solar System. Continue reading “Rosetta Flew Through the Bow Shock of Comet 67P Several Times During its Mission”
Astronomy is one of humanity’s oldest obsessions, reaching back all the way to prehistoric times. Long before the Scientific Revolution taught us that the Sun is at the center of the Solar System, or modern astronomy revealed the true extend of our galaxy and the Universe, ancient peoples were looking up at the night sky and finding patterns in the stars.
For some time, scholars believed that an understanding of complex astronomical phenomena (like the precession of the equinoxes) did not predate the ancient Greeks. However, researchers from the Universities of Edinburgh and Kent recently revealed findings that show how ancient cave paintings that date back to 40,000 years ago may in fact be astronomical calendars that monitored the equinoxes and kept track of major events.
Comet 46P Wirtanen in Cetus from September, 2018. Image credit and copyright: Hisayoshi Kato.
One. More. Comet. Though the next great ‘Comet of the Century’ has yet to make its appearance in 2018, we’ve had a steady stream of binocular comets this year, including Comets C/2017 S3 PanSTARRS, 38P Stephan-Oterma, and 21P Giacobini-Zinner.
An artist's illustration of what Phaeton might look like up close. Credit: Heather Roper/Lunar and Planetary Laboratory
Having studies countless asteroids in near-Earth space, astronomers have come to understand that the majority of these rocks fall into one of two categories: S-type (grey) and C-type (red). These are defined by the types of materials on their surfaces, with S-type asteroids being primarily composed of silicate rock and C-type asteroids being made up of carbon materials.
However, there is also what are known as blue asteroids, which make up only a fraction of all known Near-Earth Objects (NEO). But when an international team astronomers observed the blue asteroid (3200) Phaeton during a flyby of Earth, they spotted behavior that was more consistent with a blue comet. If true, then Phaeton is of a class of objects that are so rare, they are almost unheard of.
An amazing view. The Barnard loop through Orion (right) Comet 21P Giacobini-Zinner (lower left) and Comet 38P Stephan-Oterma (upper left, see enlargement below). Image credit and copyright: Hisayoshi Kato.
Artist's impression of the dead comet 2015 TB145, otherwise known as the "Death Comet" because of its appearance. Credit: José Antonio Peñas/SINC
On October 31st, 2015, NASA tracked a strange-looking comet as it made a close flyby of Earth. This asteroid, known as 2015 TB145, was monitored by the multiple observatories and radar installation of the agency’s Deep Space Network. Because of the timing and the skull-like appearance of this asteroid, scientists nicknamed it the “Death Comet”.
Naturally, there was no reason to worry, as the asteroid posed no threat and passed within about 498,900 km (310,000 mi) of Earth. But the timing and the appearance of the comet were nothing if not chilling. And coincidentally enough, the “Death Comet” (aka. “The Great Pumpkin Comet”), will be passing Earth for the second time, this time shortly after Halloween.
Comet 21P/Giacobini-Zinner from August 14th. Image credit and copyright: Rolando Ligustri.
Comet 21/P Giacobini-Zinner from August 14th. Image credit and copyright: Rolando Ligustri.
A periodic comet may put on a fine show for northern hemisphere viewers over the next few months.
Comet 21/P Giacobini-Zinner is currently a fine binocular comet, shining at +8th magnitude as it cruises across the constellation Cassiopeia. This places it above the horizon for the entire night for observers north of the equator in August, transiting the local meridian at dawn. And unlike most comets that get lost in the Sun’s glare (like the current situation with C/2017 S3 PanSTARRS), we’ll be able to track Comet 21/P Giacobini-Zinner right through perihelion on September 10th.
The orbit of comet 21P, showing the comet’s position at closest approach. Credit: NASA-JPL.
This is because the comet is on a short period, 6.6 year orbit around the Sun that takes it from an aphelion of 6 Astronomical Units (AU) exterior to Jupiter’s orbit, to a perihelion of 1.038 AU, just 3.3 million miles (5.2 million kilometers) exterior to Earth’s orbit. The 2018 apparition sees the comet pass 0.392 AU (36.5 million miles/58.3 million kilometers) from the Earth on September 11th.
This is the closest passage of the comet near Earth since September 14th, 1946, and won’t be topped until the perihelion passage of September 18th, 2058. Its next cycle of passes to Earth closer than 0.1 AU aren’t until next century in the years 2119 and 2195, respectively.
Comet 21/P from August 10th. Image credit and copyright: John Purvis.
Discovered by astronomer Michel Giacobini at the Côte d’Azur Observatory in Nice, France on the night of December 20th, 1900 as it was crossing the constellation Aquarius, the 21st periodic comet was recovered two orbits later by Ernest Zinner on October 23rd, 1913 as it passed a series of variable stars near Beta Scuti.
Though the comet generally tops out at +8th magnitude, it has been known to undergo periodic outbursts near perihelion, bringing it up about 3 magnitudes (about 16 times) in brightness. This occurred most notably in 1946.
The light curve for Comet 21/P. The black dots represent actual observations and magnitude observations. Credit: Seiichi Yoshida’sWeekly Information on Bright Comets.
Comet 21/P Giacobini-Zinner is also the source of the Draconid (sometimes referred to as the Giacobinid) meteors, radiating from the constellation Draco the Dragon on and around October 7th and 8th. Feeble on most years, this shower can produce surprises, such as occurred in 1998, 2005 and most recently in 2011, when a Draconid outburst topped a zenithal hourly rate of 400 meteors per hour, flirting with ‘meteor storm’ status. And while we’re not expecting a meteor storm to accompany the 2018 perihelion passage of Comet 21/P Giacobini-Zinner, you just never know… it’s always worth keeping an eye out on early October mornings for the “Tears of the Dragon,” just in case. Note that the Moon reaches New phase on October 9th, just a few days after the meteor shower’s expected annual peak, a fine time to watch for any unheralded Draconid outbursts.
Prospects for Comet 21P
The comet is visible from the northern hemisphere through the remainder of August and all through September as it glides across Auriga, Taurus and Gemini and visits several well known celestial sights. In fact, it actually transits in front of several deep sky objects, including Messier 37 (Sept 10th), and Messier 35 (Sept 15th).
Comet 21P passes in front of open cluster Messier 35 on September 15th. Credit: Starry Night.
The comet will be moving at about two degrees per day when it’s nearest to the Earth, on and around September 11th.
We begin to lose the comet, as it heads southward in late October. Still, the comet is over 50 degrees above the eastern horizon at dawn come October 1st as seen from latitude 30 degrees north, having maintained a similar elevation throughout most of September. Not bad at all.
Here are some upcoming dates with destiny for Comet 21/P Giacobini-Zinner:
August 19: Crosses into the constellation Camelopardalis.
August 29: Crosses into the constellation Perseus.
August 30th: Crosses into the constellation Auriga.
The celestial path of Comet 21P from August 16th through September 15th. Credit: Starry Night.
September 2: Passes one degree from the bright star Capella.
Sept 7-8: Grouped 2 degrees from the open clusters M36 and M38.
Sept 10: Photo-Op: Skirts very near the open cluster M37. Also reaches perihelion on this date, at magnitude +7.
Sept 11: Passes closest to the Earth, at 0.392 AU distant.
Sept 13: Nicks the corner of the constellation Taurus.
Sept 14th : Enters the constellation Gemini.
Sept 15th: Photo-Op: crosses in front of the open cluster M35.
Sept 16: Crosses the ecliptic southward and near the +3.3 magnitude star Propus (Eta Geminorum).
Sept 17: Crosses into Orion.
Sept 21: Crosses into Gemini.
Sept 23: Crosses into Monoceros.
Sept 24: Passes near the Christmas Tree Cluster, NGC 2264.
The celestial path of Comet 21P from September 15th through October 15th. Image credit: Starry Night.
Oct 1: Crosses the galactic plane and the celestial equator southward.
Oct 7: Crosses in front of the open cluster M50.
Oct 10: Crosses into Canis Major.
Oct 31st: Passes near the bright star Aludra and may drop below +10th magnitude.
Binoculars are your best friend when you’re looking for comets brighter than +10th magnitude. With a generous field of view, binoculars allow you to sweep a suspect area until the faint fuzzball of a comet snaps into view. I like to ‘ambush’ a comet as it passes near a bright star, and a good time to spot comet 21/P Giacobini-Zinner is coming right up on September 2nd when it passes less than one degree from the bright +0.1 magnitude star Capella.
Don’t miss this year’s fine apparition of Comet 21/P Giacobini-Zinner, coming to a night sky near you.
Comet C/2017 S3 PanSTARRS from July 22nd. Image credit and copyright: hodorgabor
Comet C/2017 S3 PanSTARRS from July 22nd. Image credit and copyright: hodorgabor
Comets are one of those great question marks in observational astronomy. Though we can plot their orbits thanks to Newton and Kepler, just how bright they’ll be and whether or not they will fizzle or fade is always a big unknown, especially if they’re a dynamic newcomer from the Oort Cloud just visiting the inner solar system for the first time.
We had just such a surprise from a cosmic visitor over the past few weeks, as comet C/2017 S3 PanSTARRSerupted twice, brightening into binocular visibility. Discovered on December 23rd 2017 during the PanSTARRS survey based on Haleakala, Hawai’i, S3 PanSTARRS is on a long-period, hyperbolic orbit and is most likely a first time visitor to the inner solar system.
The orbital path of comet S3 PanSTARRS through the inner solar system. Credit NASA/JPL.
S3 PanSTARRS was not only rocked by two new outbursts in quick succession, but seems to have undergone a tail disconnection event just last week, leveling off its brightness at around +8 magnitude and holding. This puts it in the range of binoculars under dark skies, looking like a fuzzy globular that refuses to snap into focus as it currently glides through the constellation of Camelopardalis the Giraffe the dawn sky.
The path of comet S3 PanSTARRS through August. Credit: Starry Night.
As July closes out, the time to catch sight of Comet S3 PanSTARRS is now, before it’s lost in the Sun’s glare. From latitude 40 degrees north, the comet sits 20 degrees above the northeastern horizon, about an hour before sunrise. By August 7th however, it drops below 10 degrees altitude. From there, the comet begins to circle the Sun as seen from the Earth beginning to favor southern hemisphere observers at dawn, who may be able to track it straight through perihelion on August 16th, if its brightness holds up. From there, northern hemisphere viewers may get a second view at dawn in September, again, if its brightness holds.
The dawn path of the comet looking northeast at dawn from latitude 35 degrees north, from July 31st through the first week of August. Credit: Starry Night.
You never know when it comes to comets. Here’s a brief rundown of the celestial happenings for comet C/2017 S3 PanSTARRS:
August
3- Crosses into the constellation Gemini.
4- Passes near the bright star Castor.
5- Passes near the bright star Pollux.
7- Crosses into the constellation Cancer.
7- Passes closest to the Earth, at 0.758 Astronomical Units (AU) distant.
8- Crosses southward over the ecliptic plane.
9- Passes just 4 degrees from the Beehive cluster, M44.
11- Passes 2 degrees from the open cluster M67.
12- Passes 10.5 degrees from Sun (1st apparent close pass as seen from the Earth)
13- Crosses into the constellation Hydra.
15- Reaches maximum brightness: the comet may top +2nd magnitude in mid-August.
16- Reaches perihelion at 0.21 AU from the Sun.
18- Crosses into the constellation Sextans.
30-Crosses into the constellation Leo.
31-Crosses the ecliptic plane northward.
The projected light curve for comet S3 PanSTARRS. The black dots are actual observations. Credit Seiichi Yoshida.
September
3- passes 4 degrees from the Sun.
25- Crosses into the constellation Coma Berenices.
From there, Comet C/2017 S3 PanSTARRS drops back below 6th magnitude in September, then below 10th magnitude in October as it heads back off into the icy realms of the outer solar system.
Be sure to nab this icy interloper why you can. The quote comet hunter David Levy, “Comets are like cats… they have tails, and they do exactly what they want.”
