The “Death Comet” Will Pass By Earth Just After Halloween

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.

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Catch Comet 21/P Giacobini-Zinner at Its Best

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’s Weekly 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.

Catch Comet C/2017 S3 PanSTARRS in Outburst

Comet S3 PanSTARRS
Comet S3 PanSTARRS
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 PanSTARRS erupted 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.”

70,000 Years Ago a Nearby Star Messed With the Orbits Of Comets and Asteroids in our Solar System

70,000 years ago, our keen-eyed ancestors may have noticed something in the sky: a red dwarf star that came as close as 1 light year to our Sun. They would’ve missed the red dwarf’s small, dim companion—a brown dwarf—and in any case they would’ve quickly returned to their hunting and gathering. But that star’s visit to our Solar System had an impact astronomers can still see today.

The star in question is called Scholz’s star, after astronomer Ralf-Dieter Scholz, the man who discovered it in 2013. A new study published in the Monthly Notices of the Royal Astronomical Society by astronomers at the Complutense University of Madrid, and at the University of Cambridge, shows the impact Scholz’s star had. Though the star is now almost 20 light years away, its close approach to our Sun changed the orbits of some comets and asteroids in our Solar System.

When it came to our Solar System 70,000 years ago, Scholz’s star entered the Oort Cloud. The Oort Cloud is a reservoir of mostly-icy objects that spans the range from about 0.8 to 3.2 light years from the Sun. Its visit to the Oort Cloud was first explained in a paper in 2015. This new paper follows up on that work, and shows what impact the visit had.

“Using numerical simulations, we have calculated the radiants or positions in the sky from which all these hyperbolic objects seem to come.” – Carlos de la Fuente Marcos, Complutense University of Madrid.

In this new paper, the astronomers studied almost 340 objects in our Solar System with hyperbolic orbits, which are V-shaped rather than elliptical. Their conclusion is that a significant number of these objects had their trajectories shaped by the visit from Scholz’s star. “Using numerical simulations, we have calculated the radiants or positions in the sky from which all these hyperbolic objects seem to come,” explains Carlos de la Fuente Marcos, a co-author of the study now published in Monthly Notices of the Royal Astronomical Society. They found that there’s a cluster of these objects in the direction of the Gemini Constellation.

A comparison of the Solar System and its Oort Cloud. 70,000 years ago, Scholz’s Star and companion passed along the outer boundaries of our Solar System (Credit: NASA, Michael Osadciw/University of Rochester)

“In principle,” he adds, “one would expect those positions to be evenly distributed in the sky, particularly if these objects come from the Oort cloud. However, what we find is very different—a statistically significant accumulation of radiants. The pronounced over-density appears projected in the direction of the constellation of Gemini, which fits the close encounter with Scholz’s star.”

There are four ways that objects like those in the study can gain hyperbolic orbits. They might be interstellar, like the asteroid Oumuamua, meaning they gained those orbits from some cause outside our Solar System. Or, they could be natives of our Solar System, originally bound to an elliptical orbit, but cast into a hyperbolic orbit by a close encounter with one of the planets, or the Sun. For objects originally from the Oort Cloud, they could start on a hyperbolic orbit because of interactions with the galactic disc. Finally, again for objects from the Oort Cloud, they could be cast into a hyperbolic orbit by interactions with a passing star. In this study, the passing star is Scholz’s star.

In this image the blue is a hyperbolic orbit while the green is a parabolic orbit. Image: By ScottAlanHill [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
The timing of Scholz’s star’s visit to the Oort Cloud and our Solar System strongly coincides with the data in this study. It’s very unlikely to be coincidental. “It could be a coincidence, but it is unlikely that both location and time are compatible,” says De la Fuente Marcos. In fact, De la Fuente Marcos points out that their simulations suggest that Scholz’s star approached even closer than the 0.6 light-years pointed out in the 2015 study.

The one potentially weak area of this study is pointed out by the authors themselves. As they say in their summary, “…due to their unique nature, the orbital solutions of hyperbolic minor bodies are based on relatively brief arcs of observation and this fact has an impact on their reliability. Out of 339 objects in the sample, 232 have reported uncertainties and 212 have eccentricity with statistical significance.” Translated, it means that some of the computed orbits of individual objects may have errors. But the team expects the overall conclusions of their study to be correct.

The study of minor objects with hyperbolic orbits has heated up since the interstellar asteroid Oumuamua made its visit. This new study successfully connects one population of hyperbolic objects with a pre-historic visit to our Solar System by another star. The team behind the study expects that follow up studies will confirm their results.

Rosetta’s 67P Is The Result Of A Collision Of Two Comets

Ever since we’ve been able to get closer looks at comets in our Solar System, we’ve noticed something a little puzzling. Rather than being round, they’re mostly elongated or multi-lobed. This is certainly true of Comet 67P/Churyumov-Gerasimenko (67P or Chury for short.) A new paper from an international team coordinated by Patrick Michel at France’s CNRS explains how they form this way.

The European Space Agency (ESA) spacecraft Rosetta visited 67P in 2014, end even placed its lander Philae on the surface. Rosetta spent 17 months orbiting 67P, and at its closest approach, Rosetta was only 10 km (6 mi) from 67P’s surface. Rosetta’s mission ended with its guided impact into 67P’s surface in September, 2016, but the attempt to understand the comet and its brethren didn’t end then.

An artist’s illustration of the spacecraft Rosetta and the Philae lander at comet 67P C-G. Image: By European Space Agency – Rosetta and Philae at comet, CC BY-SA 3.0-igo,

Though Rosetta’s pictures of 67P are the most detailed comet pictures we have, other spacecraft have visited other comets. And most of those other comets appear elongated or multi-lobed, too. Scientists explain these shapes with a “comet merger theory.” Two comets collide, creating the multi-lobed appearance of comets like 67P. But there’s been a problem with that theory.

In order for comets to merge and come out looking the way they do, they would have to merge very slowly, or else they would explode. They would also have to be very low-density, and be very rich in volatile elements. The “comet merger theory” also says that these types of gentle mergers between comets would have to have happened billions of years ago, in the early days of the Solar System.

The problem with this theory is, how could bodies like 67P have survived for so long? 67P is fragile, and subjected to repeated collisions in its part of the Solar System. How could it have retained its volatiles?

Geysers of dust and gas shooting off the comet’s nucleus are called jets. The volatile material they deliver outside the nucleus builds the comet’s coma. Credit: ESA/Rostta/NAVCAM

In the new paper, the research team ran a simulation that answers these questions.

The simulation showed that when two comets meet in a destructive collision, only a small portion of their material is pulverized and reduced to dust. On the sides of the comets opposite from the impact point, materials rich in volatiles withstand the collision. They’re still ejected into space, but their relative speed is low enough for them to join together in accretion. This process forms many smaller bodies, which keep clumping up until they form just one, larger body.

The most surprising part of this simulation is that this entire process may only take a few days, or even a few hours. The whole process explains how comets like 67P can keep their low density, and their abundant volatiles. And why they appear multi-lobed.

This image from the simulation shows how the ejected material from two bodies colliding re-accretes into a bilobal comet. Image: ESA/Rosetta/Navcam – CC BY-SA IGO 3.0

The simulation also answered another question: how can comets like 67P survive for so long?

The team behind the simulation thinks that the process can take place at speeds of 1 km/second. These speeds are typical in the Kuiper Belt, which is the disc of comets where 67P has its origins. In this belt, collisions between comets are a regular occurrence, which means that 67P didn’t have to form in the early days of the Solar System as previously thought. It could have formed at any time.

The team’s work also explains the surface appearance of 67P and other comets. They often have holes and stratified layers, and these features could have formed during re-accretion, or sometime after its formation.

Smooth terrain in the Imhotep region on 67P C-G, showing layering (B) and circular structures or pits (circled). Credit: ESA/Rosetta

One final point from the study concerns the composition of comets. One reason they’re a focus of such intense interest is their age. Scientists have always thought of them as ancient objects, and that studying them would allow us to look back into the primordial Solar System.

Though 67P—and other comets—may have formed much more recently than we used to believe, this process shows that there is no significant amount of heating or compaction during the collision. As a result, their original composition from the the early days of the Solar System is retained intact. No matter when 67P formed, it’s still a messenger from the formative days.

You can watch a video from the simulation here: http://www.dropbox.com/s/u7643hanvva57rp/Catastrophic%20disruptions.mp4?dl=0

The Solar System Probably has Thousands of Captured Interstellar Asteroids

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 asteroid, named 1I/2017 U1 (aka. ‘Oumuamua). Originally thought to be a comet, this interstellar visitor quickly became the focus of follow-up studies that sought to determine its origin, structure, composition, and rule out the possibility that it was an alien spacecraft!

While ‘Oumuamua is the first known example of an interstellar asteroid reaching our Solar System, scientists have long suspected that such visitors are a regular occurrence. Aiming to determine just how common, a team of researchers from Harvard University conducted a study to measure the capture rate of interstellar asteroids and comets, and what role they may play in the spread of life throughout the Universe.

The study, titled “Implications of Captured Interstellar Objects for Panspermia and Extraterrestrial Life“, recently appeared online and is being considered for publication in The Astrophysical Journal. The study was conducted by Manasavi Lingam, a postdoc at the Harvard Institute for Theory and Computation (ITC), and Abraham Loeb, the chairman of the ITC and a researcher at the Harvard-Smithsonian Center for Astrophysics (CfA).

For the sake of their study, Lingam and Loeb constructed a three-body gravitational model, where the physics of three bodies are used to compute their respective trajectories and interactions with one another. In Lingam and Loeb’s model, Jupiter and the Sun served as the two massive bodies while a far less massive interstellar object served as the third. As Dr. Loeb explained to Universe Today via email:

“The combined gravity of the Sun and Jupiter acts as a ‘fishing net’. We suggest a new approach to searching for life, which is to examine the interstellar objects captured by this fishing net instead of the traditional approach of looking through telescope or traveling with spacecrafts to distant environments to do the same.”

Using this model, the pair then began calculating the rate at which objects comparable in size to ‘Oumuamua would be captured by the Solar System, and how often such objects would collide with the Earth over the course of its entire history. They also considered the Alpha Centauri system as a separate case for the sake of comparison. In this binary system, Alpha Centauri A and B serve as the two massive bodies and an interstellar asteroid as the third.

As Dr. Lingam indicated:

“The frequency of these objects is determined from the number density of such objects, which has been recently updated based on the discovery of ‘Oumuamua. The size distribution of these objects is unknown (and serves as a free parameter in our model), but for the sake of obtaining quantitative results, we assumed that it was similar to that of comets within our Solar System.”

The theory of Lithopanspermia states that life can be shared between planets within a planetary system. Credit: NASA

In the end, they determined that a few thousands captured objects might be found within the Solar system at any time – the largest of which would be tens of km in radius. For the Alpha Centauri system, the results were even more interesting. Based on the likely rate of capture, and the maximum size of a captured object, they determined that even Earth-sized objects could have been captured in the course of the system’s history.

In other words, Alpha Centauri may have picked up some rogue planets over time, which would have had drastic impact on the evolution  of the system. In this vein, the authors also explored how objects like ‘Oumuamua could have played a role in the distribution of life throughout the Universe via rocky bodies. This is a variation on the theory of lithopanspermia, where microbial life is shared between planets thanks to asteroids, comets and meteors.

In this scenario, interstellar asteroids, which originate in distant star systems, would be the be carriers of microbial life from one system to another. If such asteroids collided with Earth in the past, they could be responsible for seeding our planet and leading to the emergence of life as we know it. As Lingam explained:

“These interstellar objects could either crash directly into a planet and thus seed it with life, or be captured into the planetary system and undergo further collisions within that system to yield interplanetary panspermia (the second scenario is more likely when the captured object is large, for e.g. a fraction of the Earth’s radius).”

In addition, Lingam and Loeb offered suggestions on how future visitors to our Solar System could be studied. As Lingam summarized, the key would be to look for specific kinds of spectra from objects in our Solar Systems:

“It may be possible to look for interstellar objects (captured/unbound) in our Solar system by looking at their trajectories in detail. Alternatively, since many objects within the Solar system have similar ratios of oxygen isotopes, finding objects with very different isotopic ratios could indicate their interstellar origin. The isotope ratios can be determined through high-resolution spectroscopy if and when interstellar comets approach close to the Sun.”

“The simplest way to single out the objects who originated outside the Solar System, is to examine the abundance ratio of oxygen isotopes in the water vapor that makes their cometary tails,” added Loeb. “This can be done through high resolution spectroscopy. After identifying a trapped interstellar object, we could launch a probe that will search on its surface for signatures of primitive life or artifacts of a technological civilization.”

It would be no exaggeration to say that the discovery of ‘Oumuamua has set off something of a revolution in astronomy. In addition to validating something astronomers have long suspected, it has also provided new opportunities for research and the testing of scientific theories (such as lithopanspermia).

In the future, with any luck, robotic missions will be dispatched to these bodies to conduct direct studies and maybe even sample return missions. What these reveal about our Universe, and maybe even the spread of life throughout, is sure to be very illuminating!

Further Reading: arXiv

This was the Snowstorm Rosetta Saw When it Got 79 km Away From Comet 67P

In August of 2014, the ESA’s Rosetta mission made history when it rendezvoused with the Comet 67P/Churyumov–Gerasimenko. For the next two years, the probe flew alongside the comet and conducted detailed studies of it. And in November of 2014, Rosetta deployed its Philae probe onto the comet, which was the first time in history that a lander was deployed to the surface of a comet.

During the course of its mission, Rosetta revealed some truly remarkable things about this comet, including data on its composition, its gaseous halo, and how it interacts with solar wind. In addition, the probe also got a good look at the endless stream of dust grains that were poured from the comet’s surface ice as it approached the Sun. From the images Rosetta captured, which the ESA just released, it looked a lot like driving through a snowstorm!

The image below was taken two years ago (on January 21st, 2016), when Rosetta was at a distance of 79 km from the comet. At the time, Rosetta was moving closer following the comet reaching perihelion, which took place during the previous August. When the comet was at perihelion, it was closer to the Sun and at its most active, which necessitated that Rosetta move farther away for its own protection.

Image of the dust and particles the Rosetta mission was exposed to as it flew alongside Comet 67P/Churyumov–Gerasimenko. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

As you can see from the image, the environment around the comet was extremely chaotic, even though it was five months after the comet was at perihelion. The white streaks reveal the dust grains as they flew in front of Rosetta’s camera over the course of a 146 second exposure. For the science team directing Rosetta, flying the spacecraft through these dust storms was like trying to drive a car through a blizzard.

Those who have tried know just how dangerous this can be! On the one hand, visibility is terrible thanks to all the flurries. On the other, the only way to stay oriented is to keep your eyes pealed for any landmarks or signs. And all the while, there is the danger of losing control and colliding with something. In much the same way, passing through the comet’s dust storms was a serious danger to the spacecraft.

In addition to the danger of collisions, flying through these clouds was also hazardous for the spacecraft’s navigation system. Like many robotic spacecraft, Rosetta relies on star trackers to orient itself – where it recognizes patterns in the field of stars to orient itself with respect to the Sun and Earth. When flying closer to the comet, Rosetta’s star trackers would occasionally become confused by dust grains, causing the craft to temporarily enter safe mode.

Artist’s impression of the Rosetta probe signalling Earth. Credits: ESA-C.Carreau

This occurred on March 28th, 2015 and again on May 30th, 2016, when Rosetta was conducting flybys that brought it to a distance of 14 and 5 km from the comet’s surface, respectively. On both occasions, Rosetta’s navigation system suffered from pointing errors when it began tracking bright dust grains instead of stars. As a result, on these occasions, the mission team lost contact with the probe for 24 hours.

As Patrick Martin, the ESA’s Rosetta mission manager, said during the second event:

“We lost contact with the spacecraft on Saturday evening for nearly 24 hours. Preliminary analysis by our flight dynamics team suggests that the star trackers locked on to a false star – that is, they were confused by comet dust close to the comet, as has been experienced before in the mission.”

Despite posing a danger to Rosetta’s solar arrays and its navigation system, this dust is also of high scientific interest. During the spacecraft’s flybys, three of its instruments studied tens of thousands of grains, analyzing their composition, mass, momentum and velocity, and also creating 3D profiles of their structure. By studying these tiny grains, scientists were also able to learn more about the bulk composition of comets.

Another snapshot of Comet 67P/Churyumov–Gerasimenko’s dusty emissions, taken on Jan. 21st, 2016. Credit: ESA

Before it reached its grand finale and crashed into the comet’s surface on September 30th, 2016, Rosetta made some unique scientific finds about the comet. These included mapping the comet’s surface features, discerning its overall shape, analyzing the chemical composition of its nucleus and coma, and measuring the ratio of water to heavy water on its surface.

All of these findings helped scientists to learn more about how our Solar System formed and evolved, and shed some light on how water was distributed throughout our Solar System early in its history. For instance, by determining that the ratio of water to heavy water on the comet was much different than that of Earth’s, scientists learned that Earth’s water was not likely to have come from comets like Comet 67P/Churyumov–Gerasimenko.

On top of that, the spacecraft took more than a hundred thousand image of the comet with its high-resolution OSIRIS camera (including the ones shown here) and its navigation camera. These images can be perused by going to the ESA’s image browser archive. I’m sure you’ll agree, they are all as beautiful as they are scientifically relevant!

Further Reading: ESA

Here Comes Comet Heinze for the Holidays

Comet C/2017 T1 Heinze passes near the galaxy NGC 2706 on November 25th. Image credit and copyright: Charles Bell.

Yeah, we’re still all waiting for that next great “Comet of the Century” to make its presence known. In the meantime, we’ve had a steady stream of good binocular comets over the past year both expected and new, including Comet C/2017 O1 ASASSN1, 45/P Honda-Mrkos-Pajdušáková and Comet 41P Tuttle-Giacobini-Kresák (links). Now, another newcomer is set to bring 2017 in over the finish line.

The Discovery: Astronomer Aren Heinze discovered Comet C/2017 T1 Heinze as a tiny +18th magnitude fuzzball on the night of October 2nd, 2017. The comet will juuust breech our “is interesting, take a look” +10th magnitude cutoff in the final weeks of December leading into January, perhaps topping out around +8th magnitude.

Heinze discovered his first comet as part of the Asteroid Terrestrial-Impact Last Alert System (ATLAS) search program looking for hazardous objects using the eight 50 cm Wright-Schmidt telescope array atop Haleakala and Mauna Loa in the Hawaiian Islands.

The passage of Comet Heinze through the inner solar system. Credit: NASA/JPL

The orbit for Comet Heinze is an intriguing one, and as is often the case with comets, tempts us with what could have been. Heinze will vault over the ecliptic headed northward on Christmas Day, and reaches perihelion 87 million km (0.58 AU) from the Sun on February 21st, 2018. Closest passage from Earth for Comet Heinze is 33 million km (0.22 AU) on January 4th, 2018, when the comet will appear to move an amazing seven degrees a day through the constellation Camelopardalis.

But it’s the southward passage of Heinze though the ecliptic on April 1st that gives us pause, only 0.0144 AU exterior of Earth’s orbit… had this occurred on July 4th, we might’ve been in for a show, with the comet only 2.1 million kilometers away! Heinze seems like a tiny body as comets go, and there’s discussion that the comet is dynamically new and may end up shredding its nucleus all together. (link)

On a steep 97 degree inclined retrograde orbit, Comet Heinze also has a knife edge hyperbolic eccentricity of nearly 1.0. As with many long period comet, it’s tough to tell if Comet Heinze is a true denizen of our solar system, or just visiting. 2017 also saw the first asteroid whose extra-solar source was clear, as I/2017 U1 ‘Oumuamua, which passed through the inner solar system this past October.

The December path of Comet Heinze. Starry Night.

The Prospects: Currently, Comet Heinze is located highest to the south around 5AM local for northern hemisphere observers. Expect this situation to change to around 2 AM towards months end, as the comet is higher placed in the constellation Lynx come January 1st, 2018 as it nears opposition.

Comet observer Charles Bell noted on November 27th that Comet Heinze currently displays a short fan-shaped tail, about 88 days before perihelion.

Here’s the blow-by-blow for Comet Heinze for the next few months (passages mentioned here are to within a degree unless otherwise noted).

December

7- Crosses the celestial equator northward.

16- Passes near +3 magnitude star Zeta Hydrae.

18- Crosses into the constellation Cancer.

21- Passes near the open cluster M67.

25- Photo op: passes near the Beehive Cluster M44 and crosses the ecliptic northward.

29- Skirts the corner of the constellation Gemini and crosses into the Lynx.

The January 2018 passage of Comet Heinze through the inner solar system. Starry Night

January

1- May break +10th magnitude?

1- Passes near the +4.5 magnitude star 21 Lyncis.

2- Reaches opposition.

3- Passes near the +4.5 magnitude star 2 Lyncis and into the constellation Camelopardalis.

5- Passes near the +4 magnitude star Alpha Camelopardalis.

6- Passes 31 degrees from the north celestial pole.

7- Crosses into the constellation Cassiopeia.

10-Crosses the galactic equator southward.

13- Crosses into the constellation Andromeda.

14-Crosses into the constellation Lacerta.

17- Passes near the +4.5 magnitude star 6 Lacertae.

21- Passes near the +4 magnitude star 1 Lacertae.

23- Crosses into the constellation Pegasus.

February

26- Passes near the globular cluster M15.

March

1- May drop back down below +10th magnitude?

heinze
The projected light curve for Comet Heinze. Credit: Seiichi Yoshida’s Weekly Info on Bright Comets.

And though Comet Heinze won’t join their ranks, here’s a list of the great comets of the past century:

You could say we’re due.

Has the First Interstellar Comet Been Discovered?

Astronomers from the Minor Planet Center sent out an announcement today, hoping for astronomers to do followup observations on the comet C/2017 U1 PANSTARRS. That’s because this strange comet seems to be on a trajectory that originated outside our Solar System. Not just from the Oort Cloud, but from another star.

Is this the first insterstellar comet ever found?

Orbital path of C 2017/U1 PANSTARRS
Orbital path of C 2017/U1 PANSTARRS

Comets are broken up into two broad categories. There are the short-period comets, the ones that started out in the Kuiper Belt and follow a regular, predictable orbit that brings them close to the Sun on a regular basis. Halley’s Comet is a great example, brightening in the skies every 7 decades or so.

The long-period comets started in the Oort Cloud, a vast collection of comets extending hundreds of astronomical units from the Sun – even out to a light-year away. These comets can take hundreds of thousands or even millions of years to make the long journey down to the inner Solar System, jostled out of their holding pattern by the interaction with a nearby star.

Astronomers make several observations of a comet’s path through the Solar System and then use this to calculate its orbital eccentricity. Zero eccentricity would orbiting the Sun in a circle, while an eccentricity of 1 would be a parabolic trajectory. Halley’s Comet, for example, has an eccentricity of 0.967; somewhere between a circle and a parabola.

From the initial observations, C/2017 U1 has an eccentricity of 1.2, which makes it a hyperbolic trajectory. This means it’s on a trajectory that came from outside the Solar System itself.

Obviously a bold claim like this requires good evidence, which is why the Minor Planet Center is looking for additional observations:

Further observations of this object are very much desired. Unless there are serious problems with much of the astrometry listed below, strongly hyperbolic orbits are the only viable solutions. Although it is probably not too sensible to compute meaningful original and future barycentric orbits, given the very short arc of observations, the orbit below has e ~ 1.2 for both values. If further observations confirm the unusual nature of this orbit, this object may be the first clear case of an interstellar comet.

In a tweet, astronomer Tony Dunn included a simulation he’d made showing the trajectory of C/2017 U1 compared to other comets discovered this year.

How could a comet like this have gotten to the Solar System? When other stars pass within a few light-years of the Sun, they stir up our Oort Cloud with their gravity. Presumably the Sun does the same to other stars system cometary clouds. Three-body interactions between the comet, planets and the star could kick a comet out into an escape orbit from its star system. Actually, astronomers are arguing about the possible source in the Minor Planet Mailing List group.

Again, Tony Dunn simulated its current trajectory, showing how the comet would have been flying towards us from the Constellation Lyrae, which contains the bright star Vega. Did it come from Vega? We’ll probably never know.

C/2017 U1 was first discovered on October 18, 2017 from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) located at the Haleakala Observatory in Hawaii. The purpose of this automated telescope is to scan the sky night after night, searching for moving and variable objects. It’s one of the most prolific comet hunters in the world, which is why you probably see so many comets named after it.

The comet was about 30 million kilometers (19 million miles) from Earth, and only 6 days of observations have been made. It was traveling at a velocity of 26 km/s, much faster than the escape velocity of the Solar System.

We now know that it passed its closest point to the Sun on September 9, 2017, and is well on its way back out of the Solar System.

Will this turn out to be the first interstellar comet? It’s already as dim as magnitude 21, so astronomers will need to work quickly to gather more observations before it fades from sight entirely.

Source: Minor Planet Center