70,000 years ago, Scholz's star, a red dwarf, came as close as 1 light year to our Solar System. At that time, neanderthals were still around. Image: Credit: José A. Peñas/SINC
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 CommonsThe 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.
The comet 67P/Churyumov-Gerasimenko, which was visited by Rosetta in 2014-15, certainly appears to be the result of a collision between two comets. A new study explains how and when the collision occurred. By ESA/Rosetta/OSIRIS - http://www.esa.int/spaceinimages/Images/2014/12/Colour_image_of_comet, CC BY-SA 3.0,
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.
Artist’s impression of the first interstellar asteroid/comet, "Oumuamua". This unique object was discovered on 19 October 2017 by the Pan-STARRS 1 telescope in Hawaii. Credit: ESO/M. Kornmesser
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.
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!
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 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.
“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!
Comet C/2017 T1 Heinze passes near the galaxy NGC 2706 on November 25th. Image credit and copyright: Charles Bell.
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?
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:
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
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.
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.
Is comet #C2017U1 a visitor from another solar system? Here's a simulation of its current nominal orbit. This simulation will run in your browser. https://t.co/M1O5an87qk Watch how fast it moves compared to a few other 2017 comet discoveries. pic.twitter.com/cq7U5eYKOu
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.
Did it come from Vega?
Here are 2 more simulations of #C2017U1. They will run in your browser.
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.
Where Do Comets Come From? Exploring the Oort Cloud
Before I get into this article, I want to remind everyone that it’s been several decades since I’ve been able to enjoy a bright comet in the night sky. I’ve seen mind blowing auroras, witnessed a total solar eclipse with my own eyeballs, and seen a rocket launch. The Universe needs to deliver this bright comet for me, and it needs to do it soon.
By writing this article now, I will summon it. I will create an article that’ll be hilariously out of date in a few months, when that bright comet shows up.
Anyway, on to the article. Let’s talk about comets.
Comet C/2014 Q2 Lovejoy, Widefield view, false color. Feb 8, 2015. Credit and copyright: Joseph Brimacombe.
Comets are awesome. They’re made of gas, dust, rock, and organic materials, smashed together, and existing mostly unchanged since the formation of the Solar System 4.5 billion years ago. Every now and then, some gravitational interaction kicks a comet into an orbit that brings it closer to the Sun.
Because of the increased radiation, the comet’s volatile gas and dust sublimates off the surface, leaving behind a long tail of ice. And this is how we discover them.
In fact, comets are one of the objects in the night sky regularly found by amateurs. And by discovering a comet, you get to have it named after you. Of course many of the comets are named after robotic observatories, just another way the robots are taking human jobs.
The source of comets was originally proposed by Gerard Kuiper in 1951, when he theorized that there must be a vast disk of gas and dust surrounding the Solar System, out beyond the orbit of Pluto.
This “Kuiper Belt”, contains millions of objects, which orbit the Sun, jostling each other with their gravity. These interactions kick these Kuiper Belt comets into orbits that bring them closer to the Sun, where they get their characteristic tails.
Astronomers call these short period comets, since they orbit the Sun relatively often. They’re given names and designations, and astronomers can calculate when the comet will pass near to the Sun and flare up again.
Halley’s Comet, as seen by the European Giotto probe. Credit: Halley Multicolor Camera Team, Giotto Project, ESA
The famous Halley’s Comet is a good example, which was known to antiquity, but had its orbit first calculated in 1705 by Edmond Halley. Every 74 to 79 years, Halley’s Comet swings near the Sun, flares up and we get a view of this amazing object. It last passed our area in 1986, and it’s not due to return until 2061. I should be in my third robot body by then.
The long period comets are much more mysterious. These objects come out of nowhere, pass through the inner Solar System or smash into the Sun, and then zip back out into deep space. Now, where do they come from?
The Dutch astronomer Jan Oort calculated that there must be an even vaster cloud of ice even farther out beyond the Kuiper Belt – between 5,000 and 100,000 astronomical units from the Sun. Just a reminder, 1 astronomical unit is the distance from the Earth to the Sun, so we’re talking really really far away. The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA
Like, the Voyager 1 spacecraft, which is the most distant and fastest object ever sent out by humanity, will still need about 300 years to reach the edge of the Oort Cloud.
Astronomers think that occasional gravitational nudges in the Oort Cloud cause these long period comets to fall down into the inner Solar System and make their rare appearances. It could take a comet like this hundreds of thousands or even millions of years to complete an orbit around the Sun. I’ll need a few dozen robot bodies for that repeat observation.
Check out this cool picture of Comet C/2017 K2 PANSTARRS, taken by the Hubble Space Telescope. This is a great example of a long-period comet, which is visiting our neighbourhood for the first time in the 4.5 billion-year history of the Solar System.
This is the dimmest, farthest comet ever discovered, first seen when it was out beyond the orbit of Saturn.
This cloud of material around the comet is probably the sublimation of frozen volatile gases, like oxygen, nitrogen, carbon dioxide and carbon monoxide. Astronomers think it started to become active about 4 years ago, and they just discovered it now.
As it gets closer to the Sun and warms up, it’ll become a true comet, when its hard-as-rock water ice structure starts to sublimate and earns its tail.
It should make its closest approach in 2022 when it gets about as close to the Sun as Mars.
And this is why we can’t detect out into the Oort Cloud yet. We can barely detect comets outside the orbit of Saturn, not to mention hundreds of times farther than that.
Our Sun isn’t alone in the Milky Way, obviously. It’s a vast swirling storm of hundreds of billions of stars, and over the tens of thousand of years, other stars come much closer to the Sun than we see today.
The European Space Agency’s Gaia spacecraft recently released one of the most detailed maps of stellar positions and motions, and gave us a much better picture of where our Sun is going, and what it’s going to be interacting with in the future.
In order to interact with the Oort Cloud, astronomers have calculated that a star needs to get within about 6.5 light years before it can interact gravitationally, depending on its mass. Credit: ESA / Gaia / DPAC / A. Moitinho & M. Barros, CENTRA – University of Lisbon.
Based on data gathered by the Gaia spacecraft, astronomers charted out the motions of 300,000 stars in our vicinity of the Milky Way in the next 5 million years or so.
Of those stars, 97 will come within 15 light-years of the Sun, and 16 will get closer than 6.5. The most interesting of these is Gliese 710. In 1.3 million years, it’ll pass less than 2.5 light-years away from the Sun, plunging right through the Oort Cloud.
Gliese 710 has about 60% the mass of the Sun, and it’s going about half the speed that stars normally go as they sweep past the Solar System. Which means that it’s going to stick around for a long time, pushing comets around with its mass, and send showers of comets down into the Solar System.
On average, it seems like a star passes within 15 light-years every 50,000 years or so, jostling up our collection of comets.
This is important, because comet impacts could be a cause of past extinction events on Earth. By tracking the movements of stars in our region, astronomers could try to match up past events with times that stars jostled up the Oort Cloud, and predict future events.
Could we ever reach the Oort Cloud and explore it? A few years ago, a space observatory was proposed that could attempt to observe objects as distant as the Oort Cloud. Known as the Whipple Mission, it would orbit in the Sun-Earth L2 point, and watch the sky with a wide field of view.
It would try to detect transiting events when objects as small as a kilometer across passed in front of a more distant star. In theory, the mission would be capable of spotting these transits out as far as 22,000 astronomical units or nearly half a light year. Unfortunately, it hasn’t gotten past the proposal stage. How the FOCAL mission would see a terrestrial planet. Credit: Geoffrey A. Landis
Another intriguing idea is known as the FOCAL mission, which involves sending a space telescope out to a distance of 550 astronomical units away from the Sun. At this point, the telescope can use the gravity of the Sun itself as an enormous lens, focusing the light from more distant objects.
Actually, you’d need to go farther. At 550 astronomical units, the sunlight drowns out anything the space telescope might try to see. Instead, it needs to go out to a distance of more than 2,000 astronomical units from Earth, when the light focused by the Sun turns into an Einstein Ring around it.
What could you do with a telescope like this? If an exoplanet were to pass behind the Sun, perfectly lined up, you could resolve features as small as 1 kilometer across on a world 35 light-years away.
A telescope like this gives us a very good reason to learn to travel out and explore the Oort Cloud.
The Gaia spacecraft is still hard at work gathering data, and astronomers are expecting another massive data dump in April, 2018. Over time, the spacecraft will map out the position and movements of a billion stars in the Milky Way.
Comets are awesome, and I’d like to see a visible comet in the night sky, but I’d like them to keep their distance.
A final image from Rosetta, shortly before it made a controlled impact onto Comet 67P/Churyumov–Gerasimenko on 30 September 2016. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.
ESA scientists have found one additional image from the Rosetta spacecraft hiding in the telemetry. This new image was found in the last bits of data sent by Rosetta immediately before it shut down on the surface of Comet 67P/Churyumov–Gerasimenko last year.
The new image shows a close-up shot of the rocky, pebbly surface of the comet, and looks somewhat reminiscent of the views the Huygens lander took of the surface of Saturn’s moon Titan. A final image from Rosetta, shortly before it made a controlled impact onto Comet 67P/Churyumov–Gerasimenko on 30 September 2016. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.
Planetary astronomer Andy Rivkin noted on Twitter that for size context, he estimates the block just right of center looks to be about the size of a hat. That’s a fun comparison to have (not to mention thinking about hats on Comet 67P!)
The picture has a scale of 2 mm/pixel and measures about 1 m across. It’s a really ‘close’ close-up of Comet 67P.
“The last complete image transmitted from Rosetta was the final one that we saw arriving back on Earth in one piece moments before the touchdown at Sais,” said Holger Sierks, principal investigator for the OSIRIS camera at the Max Planck Institute for Solar System Research in Göttingen, Germany. “Later, we found a few telemetry packets on our server and thought, wow, that could be another image.”
The team explains that the image data were put into telemetry ‘packets’ aboard Rosetta before they were transmitted to Earth, and the final images were split into six packets. However, for the very last image, the transmission was interrupted after only three full packets. The incomplete data was not recognized as an image by the automatic processing software, but later, the engineers in Göttingen could make sense of these data fragments to reconstruct the image.
You’ll notice it is rather blurry. The OSIRIS camera team says this image only has about 53% of the full data and “therefore represents an image with an effective compression ratio of 1:38 compared to the anticipated compression ratio of 1:20, meaning some of the finer detail was lost.”
That is, it gets a lot blurrier as you zoom in compared with a full-quality image. They compared it to compressing an image to send via email, versus an uncompressed version that you would print out and hang on your wall.
Rosetta’s final resting spot is in a region of active pits in the Ma’at region on the two-lobed, duck-shaped comet.
A montage of the last few images from Rosetta, including the new image, with context of where the features on the last images are located. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Launched in 2004, Rosetta traveled nearly 8 billion kilometers and its journey included three Earth flybys and one at Mars, and two asteroid encounters. It arrived at the comet in August 2014 after being in hibernation for 31 months.
After becoming the first spacecraft to orbit a comet, it deployed the Philae lander in November 2014. Philae sent back data for a few days before succumbing to a power loss after it unfortunately landed in a crevice and its solar panels couldn’t receive sunlight.
But Rosetta showed us unprecedented views of Comet 67P and monitored the comet’s evolution as it made its closest approach and then moved away from the Sun. However, Rosetta and the comet moved too far away from the Sun for the spacecraft to receive enough power to continue operations, so the mission plan was to set the spacecraft down on the comet’s surface.
And scientists have continued to sift through the data, and this new image was found. Who knows what else they’ll find, hiding the data?
A new study indicates that in about a million years, a star will pass close to our Solar System, sending comets towards Earth and the other planets. Credit: NASA/JPL-Caltech
To our Solar System, “close-encounters” with other stars happen regularly – the last occurring some 70,000 years ago and the next likely to take place 240,000 to 470,000 years from now. While this might sound like a “few and far between” kind of thing, it is quite regular in cosmological terms. Understanding when these encounters will happen is also important since they are known to cause disturbances in theOort Cloud, sending comets towards Earth.
Thanks to a new study by Coryn Bailer-Jones, a researcher from the Max Planck Institute for Astronomy, astronomers now have refined estimates on when the next close-encounters will be happening. After consulting data from the ESA’s Gaia spacecraft, he concluded that over the course of the next 5 million years, that the Solar System can expect 16 close encounters, and one particularly close one!
Artist’s impression of the ESA’s Gaia spacecraft. Credit: ESA/ATG medialab; background: ESO/S. Brunier
As noted, these types of disturbances have happened many times throughout the history of the Solar System. In order to dislodge icy objects from their orbit in the Oort Cloud – which extends out to about 15 trillion km (100,000 AU) from our Sun – and send them hurling into the inner Solar System, it is estimated that a star would need to pass within 60 trillion km (37 trillion mi; 400,000 AU) of our Sun.
While these close encounters pose no real risk to our Solar System, they have been known to increase comet activity. As Dr. Bailer-Jones explained to Universe Today via email:
“Their potential influence is to shake up the Oort cloud of comets surrounding our Sun, which could result in some being pushed into the inner solar system where is chance they could impact with the Earth. But the long-term probability of one such comet hitting the Earth is probably lower than the probability the Earth is hit by a near-Earth asteroid. So they don’t pose much more danger.”
One of the goals of the Gaia mission, which launched back in 2013, was to collect precise data on stellar positions and motions over the course of its five-year mission. After 14 months in space, the first catalogue was released, which contained information on more than a billion stars. This catalogue also contained the distances and motions across the sky of over two million stars.
By combining this new data with existing information, Dr. Bailer-Jones was able to calculate the motions of some 300,000 stars relative to the Sun over a five million year period. As he explained:
“I traced the orbits of stars observed by Gaia (in the so-called TGAS catalogue) backwards and forwards in time, to see when and how close they would come to the Sun. I then computed the so-called ‘completeness function’ of TGAS to find out what fraction of encounters would have been missed by the survey: TGAS doesn’t see fainter stars (and the very brightest stars are also omitted at present, for technical reasons), but using a simple model of the Galaxy I can estimate how many stars it is missing. Combining this with the actual number of encounters found, I could estimate the total rate of stellar encounters (i.e. including the ones not actually seen). This is necessarily a rather rough estimate, as it involves a number of assumptions, not least the model for what is not seen.”
From this, he was able to come up with a general estimate of the rate of stellar encounters over the past 5 million years, and for the next 5 million. He determined that the overall rate is about 550 stars per million years coming within 150 trillion km, and about 20 coming closer than 30 trillion km. This works out to about one potential close encounter every 50,000 years or so.
Dr. Bailor-Jones also determined that of the 300,000 stars he observed, 97 of them would pass within 150 trillion km (93 trillion mi; 1 million AU) of our Solar System, while 16 would come within 60 trillion km. While this would be close enough to disturb the Oort Cloud, only one star would get particularly close. That star is Gliese 710, a K-type yellow dwarf located about 63 light years from Earth which is about half the size of our Sun.
Stars speeding through the Galaxy. Credit: ESA
According to Dr. Bailer-Jones’ study, this star will pass by our Solar System in 1.3 million years, and at a distance of just 2.3 trillion km (1.4 trillion mi; 16 ,000AU). This will place it well within the Oort Cloud, and will likely turn many icy planetesimals into long-period comets that could head towards Earth. What’s more, Gliese 710 has a relatively slow velocity compared to other stars in our galaxy.
Whereas the average relative velocity of stars is estimated to be around 100.000 km/h (62,000 mph) at their closest approach, Gliese 710 will will have a speed of 50,000 km/h (31,000 mph). As a result, the star will have plenty of time to exert its gravitational influence on the Oort Cloud, which could potentially send many, many comets towards Earth and the inner Solar System.
Over the past few decades, this star has been well-documented by astronomers, and they were already pretty certain that it would experience a close encounter with our Solar System in the future. However, previous calculations indicated that it would pass within 3.1 to 13.6 trillion km (1.9 to 8.45 trillion mi; 20,722 to 90,910 AU) from our star system – and with a 90% certainty. Thanks to this most recent study, these estimates have been refined to 1.5–3.2 trillion km, with 2.3 trillion km being the most likely.
Again, while it might sound like these passes are on too large of a timescale to be of concern, in terms of the astronomical history, its a regular occurrence. And while not every close encounter is guaranteed to send comets hurling our way, understanding when and how these encounters have happened is intrinsic to understanding the history and evolution of our Solar System.
Understanding when a close encounters might happen next is also vital. Assuming we are still around when another takes place, knowing when it is likely to happen could allow us to prepare for the worst – i.e. if a comets is set on a collision course with Earth! Failing that, humanity could use this information to prepare a scientific mission to study the comets that are sent our way.
The second release of Gaia data is scheduled for next April, and will contain information on an estimated 1 billion stars. That’s 20 times as many stars as the first catalogue, and about 1% the total number of stars within the Milky Way Galaxy. The second catalog will also include information on much more distant stars, will which allow for reconstructions of up to 25 million years into the past and future.
As Dr. Bailer-Jones indicated, the release of Gaia data has helped astronomers considerably. “[I]t greatly improves on what we had before, in both number of stars and precision,” he said. “But this is really just a taster of what will come in the second data release in April 2018, when we will provide parallaxes and proper motions for around one billion stars (500 times as many as in the first data release).”
With every new release, estimates on the movements of the galaxy’s stars (and the potential for close encounters) will be refined further. It will also help us to chart when major comet activity took place within the Solar System, and how this might have played a role in the evolution of the planets and life itself.
A new comet discovery crept up on us this past weekend, one that should be visible for northern hemisphere observers soon.
We’re talking about Comet C/2017 O1 ASAS-SN, a long period comet currently visiting the inner solar system. When it was discovered on July 19th, 2017 by the All Sky Automated Survey for Supernovae (ASAS-SN) system, Comet O1 ASAS-SN was at a faint magnitude +15.3 in the constellation Cetus. In just a few short days, however, the comet jumped up a hundred-fold in brightness to magnitude +10, and should be in range of binoculars now. Hopes are up that the comet will top out around magnitude +8 or so in October, as it transitions from the southern to northern hemisphere.
Never heard of ASAS-SN? It’s an automated sky survey hunting for supernovae in both hemispheres, with instruments based at Haleakala in Hawaii and Cerro Tololo in Chile. Though the survey targets supernovae, it does on occasion pick up other interesting astronomical phenomena as well. This is the first comet discovery for the ASAS-SN team, as they join the ranks of PanSTARRS, LINEAR and other prolific robotic comet hunters.
Evoking the very name “ASAS-SN” seems to have sparked a minor controversy as well, as the International Astronomical Union (IAU) declined to name the comet after the survey, listing it simply as “C/2017 O1”. Word is, “ASAS-SN” was to close to the word “Assassin” (this is actually controversial?) For our money, we’ll simply keep referring to the comet as “O1 ASAS-SN” as a recognition of the team’s hard work and their terrific discovery.
The orbit of Comet C/2017 O1 ASAS-Sn through the inner solar system. Credit: NASA/JPL
But what’s in a name, and does an interplanetary iceball really care? On a long term parabolic orbit probably measured in the millions of years, O1 ASAS-SN has an orbit inclined 40 degrees to the ecliptic, and reaches perihelion 1.5 AU from the Sun just outside the orbit of Mars on October 14th. This is most likely Comet C/2017 O1 ASAS-SN’s first passage through the inner solar system.
Currently located in the constellation Eridanus, hopefully comet O1 ASAS-SN’s current outburst holds. Expect it to climb northward through Taurus and Perseus over the next few months as it begins the long climb towards the north celestial pole.
Anatomy of an outburst: Comet ASAS-SN shortly after discovery over the span of a week. Credit ASAS-SN1.
As seen from latitude 30 degrees north, the comet will move almost parallel to the eastern horizon, and clears about 20 degrees altitude around local midnight, very well placed for northern hemisphere observers.
The path of Comet C/2017 O1 ASAS-SN parallel to the eastern horizon through September as seen from latitude 30 degrees north. Credit: Stellarium
At its closest in mid-October, Comet O1 ASAS-SN will be moving a degree a day through the constellation Camelopardalis
Here’s a month-by-month blow by blow for Comet O1 ASAS-SN:
August
14- Crosses into Cetus.
16- Crosses the celestial equator northward.
20- Crosses into Taurus.
The celestial path of Comet C/2017 O1 ASAS-SN from late July through mid-October (click to enlarge). Credit: Starry Night.
September
11-The waning gibbous Moon passes two degrees to the south.
17- Crosses the ecliptic northward.
20- Photo op: passes 4 degrees from the Pleiades open star cluster (M45).
28-Crosses into Perseus.
The projected light curve for Comet C/2017 O1 ASAS-SN. Note the outburst from actual observations (black dots). Credit: Seiichi Yoshida’s Weekly Information About Bright Comets.
October
1-Reaches max brightness?
12-Crosses the galactic equator northward.
14-Reaches perihelion 1.5 AU from the Sun.
17-Crosses into Camelopardalis.
18- Passes closest to Earth at 0.722 AU distant.
29-Passes 10′ from the +4 mag star Alpha Camelopardalis.
November
17-Crosses into Cepheus
December
6-Passes 3 degrees from the north celestial pole.
12-Reaches opposition.
31-Drops back down below +10th magnitude
At the eyepiece, a small comet generally looks like a small fuzzy globular cluster that refuses to snap into focus. Seek out dark skies in your cometary quest, as the least bit of light pollution will dim it below visibility. And speaking of which, the Moon is also moving towards Full next week so the time to hunt for the comet is now.
Keep in mind, current magnitude estimates for Comet O1 ASAS-SN are still highly speculative, as we seem to have caught this one in outburst… hey, remember Comet Holmes back about a decade ago in 2007? One can only dream!
-Also check out this recent NEOWISE study suggesting that large long period comets may be more common that generally thought.
