Alas, all good things must come to an end. In 2020, Arianespace and the ESA signed contracts for the rocket’s last eight launches before the Ariane 6 (a heavier two-stage launcher) would succeed it. The Ariane 5‘s final flight (VA261) lifted off from Europe’s Spaceport at 06:00 PM EST (03:00 PM PST) on July 5th, 2023, and placed two payloads into their planned geostationary transfer orbits (GTO) about 33 minutes later. On the downside, this means that the ESA is effectively out of launch vehicles until the Ariane 6 makes its debut next year.
The ESA’s Rosetta mission to Comet 67P/Churyumov-Gerasimenko ended four years ago. On September 30th 2016 the spacecraft was directed into a controlled impact with the comet, putting an end to its 12.5 year mission. Scientists are still working with all its data and making new discoveries.
A new study based on Rosetta data shows that Comet 67P has its own aurora.
Why is there so little nitrogen in Comet 67P/Churyumov-Gerasimenko (67P)? That’s a question scientists asked themselves when they looked at the data from the ESA’s Rosetta spacecraft. In fact, it’s a question they ask themselves every time they measure the gases in a comet’s coma. When Rosetta visited the comet in 2014, it measured the gases and found that there was very little nitrogen.
In two new papers published in Nature Astronomy, researchers suggest that the nitrogen isn’t really missing at all, it’s just hidden in the building blocks of life.
It seems that comet 67P/Churyumov–Gerasimenko is not the stoic, unchanging Solar System traveller that it might seem to be. Scientists working through the vast warehouse of images from the Rosetta spacecraft have discovered there’s lots going on on 67P. Among the activity are collapsing cliffs and bouncing boulders.
The European Space Agency’s (ESA) Rosetta mission spent two years at the comet 67P/Churyumov-Gerasimenko. At the end of September 2016, its mission was ended when the spacecraft was sent on a collision course into the comet. During its time at comet 67P, it captured a vast amount of images.
The ESA made all those images freely available at their Rosetta website, and now an astro-photographer working with those images has found something interesting: a chunk of ice travelling through space with 67P.
In 2014 , the European Space Agency’s (ESA) Rosetta spacecraft made history when it rendezvoused with Comet 67P/Churyumov-Gerasimenko. This mission would be the first of its kind, where a spacecraft intercepted a comet, followed it as it orbited the Sun, and deployed a lander to its surface. For the next two years, the orbiter would study this comet in the hopes of revealing things about the history of the Solar System.
The European Space Agency’s Rosetta mission was an ambitious one. As the first-ever space probe to rendezvous with and then orbit a comet, Rosetta and its lander (Philae) revealed a great deal about the comet 67p/Churyumov-Gerasimenko. In addition to the learning things about the comet’s shape, composition and tail, the mission also captured some incredible images of the comet’s surface before it ended.
For instance, Rosetta took a series of images on June 1st, 2016, that showed what looks like a blizzard on the comet’s surface. Using these raw images (which were posted on March 22nd, 2018), twitter user landru79 created an eye-popping video that shows just what it would be like to stand on the comet’s surface. As you can see, its like standing in a blizzard on Earth, though scientists have indicated that it’s a little more complicated than that.
The video, which consists of 25 minutes worth of images taken by Rosetta’s Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS), was posted by landru79 on April 23rd, 2018. It shows the surface of 67p/Churyumov-Gerasimenko on the loop, which lends it the appearance of panning across the surface in the middle of a snowstorm.
However, according to the ESA, the effect is likely caused by three separate phenomena. For instance, the snow-like particles seen in the video are theorized to be a combination of dust from the comet itself as well as high-energy particles striking the camera. Because of OSIRIS’ charge-coupled device (CCD) – a radiation-sensing camera – even invisible particles appear like bright streaks when passing in front of it.
As for the white specks in the background, those are stars belonging to the Canis Major constellation (according to ESA senior advisor Mark McCaughrean). Since originally posting the video, landru79 has posted another GIF on Twitter (see below) that freezes the starfield in place. This makes it clearer that the comet is moving, but the stars are remaining still (at least, relative to the camera’s point of view).
And of course, the entire video has been sped up considerably for dramatic effect. According to a follow-up tweet posted by landru79, the first image was shot on June 1st, 2016 at 3.981 seconds past 17:00 (UTC) while the last one was shot at 170.17 seconds past 17:25.
Si apilamos todo el set alineando con las estrellas de fondo se distingue mejor que son estrellas y q es polvo (olvidaos de rayos cósmicos ) #ROSETTA ? OSIRIS #67P/CHURYUMOV-GERASIMENKO new albums ?–ROSETTA EXTENSION 2 MTP030– Miércoles 1 Junio 2016 all filters stacked? pic.twitter.com/UyZ628JxKP
Still, one cannot deny that it is both captivating and draws attention to what Rosetta the mission accomplished. The mission launched in 2004 and reached 67P/Churyumov-Gerasimenko in 2014. After two years of gathering data, it was deliberately crashed on its surface in 2016. And yet, years later, what it revealed is still captivating people all over the world.
In the 18th century, observations made of all the known planets (Mercury, Venus, Earth, Mars, Jupiter, and Saturn) led astronomers to discern a pattern in their orbits. Eventually, this led to the Titius–Bode Law, which predicted the amount of space between the planets. In accordance with this law, there appeared to be a discernible gap between the orbits of Mars and Jupiter, and investigation into it led to a major discovery.
In addition to several larger objects being observed, astronomers began to notice countless smaller bodies also orbiting between Mars and Jupiter. This led to the creation of the term “asteroid”, as well as “Asteroid Belt” once it became clear just how many there were. Since that time, the term has entered common usage and become a mainstay of our astronomical models.
In 1800, hoping to resolve the issue created by the Titius-Bode Law, astronomer Baron Franz Xaver von Zach recruited 24 of his fellow astronomers into a club known as the “United Astronomical Society” (sometimes referred to the as “Stellar Police”). At the time, its ranks included famed astronomer William Herschel, who had discovered Uranus and its moons in the 1780s.
Ironically, the first astronomer to make a discovery in this regions was Giuseppe Piazzi – the chair of astronomy at the University of Palermo – who had been asked to join the Society but had not yet received the invitation. On January 1st, 1801, Piazzi observed a tiny object in an orbit with the exact radius predicted by the Titius-Bode law.
Initially, he believed it to be a comet, but ongoing observations showed that it had no coma. This led Piazzi to consider that the object he had found – which he named “Ceres” after the Roman goddess of the harvest and patron of Sicily – could, in fact, be a planet. Fifteen months later, Heinrich Olbers ( a member of the Society) discovered a second object in the same region, which was later named 2 Pallas.
In appearance, these objects seemed indistinguishable from stars. Even under the highest telescope magnifications, they did not resolve into discs. However, their rapid movement was indicative of a shared orbit. Hence, William Herschel suggested that they be placed into a separate category called “asteroids” – Greek for “star-like”.
By 1807, further investigation revealed two new objects in the region, 3 Juno and 4 Vesta; and by 1845, 5 Astraea was found. Shortly thereafter, new objects were found at an accelerating rate, and by the early 1850s, the term “asteroids” gradually came into common use. So too did the term “Asteroid Belt”, though it is unclear who coined that particular term. However, the term “Main Belt” is often used to distinguish it from the Kuiper Belt.
One hundred asteroids had been located by mid-1868, and in 1891 the introduction of astrophotography by Max Wolf accelerated the rate of discovery even further. A total of 1,000 asteroids were found by 1921, 10,000 by 1981, and 100,000 by 2000. Modern asteroid survey systems now use automated means to locate new minor planets in ever-increasing quantities.
Despite common perceptions, the Asteroid Belt is mostly empty space, with the asteroids spread over a large volume of space. Nevertheless, hundreds of thousands of asteroids are currently known, and the total number ranges in the millions or more. Over 200 asteroids are known to be larger than 100 km in diameter, and a survey in the infrared wavelengths has shown that the asteroid belt has 0.7–1.7 million asteroids with a diameter of 1 km (0.6 mi) or more.
Located between Mars and Jupiter, the belt ranges from 2.2 to 3.2 astronomical units (AU) from the Sun and is 1 AU thick. Its total mass is estimated to be 2.8×1021 to 3.2×1021 kilograms – which is equivalent to about 4% of the Moon’s mass. The four largest objects – Ceres, 4 Vesta, 2 Pallas, and 10 Hygiea – account for half of the belt’s total mass, with almost one-third accounted for by Ceres alone.
The main (or core) population of the asteroid belt is sometimes divided into three zones, which are based on what is known as Kirkwood Gaps. Named after Daniel Kirkwood, who announced in 1866 the discovery of gaps in the distance of asteroids, these describe the dimensions of an asteroid’s orbit based on its semi-major axis.
Within this scheme, there are three zones. Zone I lies between the 4:1 resonance and 3:1 resonance Kirkwood gaps, which are 2.06 and 2.5 AU from the Sun respectively. Zone II continues from the end of Zone I out to the 5:2 resonance gap, which is 2.82 AU from the Sun. Zone III extends from the outer edge of Zone II to the 2:1 resonance gap at 3.28 AU.
The asteroid belt may also be divided into the inner and outer belts, with the inner belt formed by asteroids orbiting nearer to Mars than the 3:1 Kirkwood gap (2.5 AU), and the outer belt formed by those asteroids closer to Jupiter’s orbit.
The asteroids that have a radius of 2.06 AU from the Sun can be considered the inner boundary of the asteroid belt. Perturbations by Jupiter send bodies straying there into unstable orbits. Most bodies formed inside the radius of this gap were swept up by Mars (which has an aphelion at 1.67 AU) or ejected by its gravitational perturbations in the early history of the Solar System.
The temperature of the Asteroid Belt varies with the distance from the Sun. For dust particles within the belt, typical temperatures range from 200 K (-73 °C) at 2.2 AU down to 165 K (-108 °C) at 3.2 AU. However, due to rotation, the surface temperature of an asteroid can vary considerably as the sides are alternately exposed to solar radiation and then to the stellar background.
Much like the terrestrial planets, most asteroids are composed of silicate rock while a small portion contains metals such as iron and nickel. The remaining asteroids are made up of a mix of these, along with carbon-rich materials. Some of the more distant asteroids tend to contain more ices and volatiles, which includes water ice.
The Main Belt consists primarily of three categories of asteroids: C-type, or carbonaceous asteroids; S-type, or silicate asteroids; and M-type, or metallic asteroids. Carbonaceous asteroids are carbon-rich, dominate the belt’s outer regions, and comprise over 75% of the visible asteroids. Their surface composition is similar to that of carbonaceous chondrite meteorites while their spectra is similar to what the early Solar System’s is believed to be.
S-type (silicate-rich) asteroids are more common toward the inner region of the belt, within 2.5 AU of the Sun. These are typically composed of silicates and some metals, but not a significant amount of carbonaceous compounds. This indicates that their materials have been modified significantly over time, most likely through melting and reformation.
M-type (metal-rich) asteroids form about 10% of the total population and are composed of iron-nickel and some silicate compounds. Some are believed to have originated from the metallic cores of differentiated asteroids, which were then fragmented from collisions. Within the asteroid belt, the distribution of these types of asteroids peaks at a semi-major axis of about 2.7 AU from the Sun.
There’s also the mysterious and relatively rare V-type (or basaltic) asteroids. This group takes their name from the fact that until 2001, most basaltic bodies in the Asteroid Belt were believed to have originated from the asteroid Vesta. However, the discovery of basaltic asteroids with different chemical compositions suggests a different origin. Current theories of asteroid formation predict that the V-type asteroids should be more plentiful, but 99% of those that have been predicted are currently missing.
Families and Groups:
Approximately one-third of the asteroids in the asteroid belt are members of an asteroid family. These are based on similarities in orbital elements – such as semi-major axis, eccentricity, orbital inclinations, and similar spectral features, all of which indicate a common origin. Most likely, this would have involved collisions between larger objects (with a mean radius of ~10 km) that then broke up into smaller bodies.
Some of the most prominent families in the asteroid belt are the Flora, Eunomia, Koronis, Eos, and Themis families. The Flora family, one of the largest with more than 800 known members, may have formed from a collision less than a billion years ago. Located within the inner region of the Belt, this family is made up of S-type asteroids and accounts for roughly 4-5% of all Belt objects.
The Eunomia family is another large grouping of S-type asteroids, which takes its name from the Greek goddess Eunomia (goddess of law and good order). It is the most prominent family in the intermediate asteroid belt and accounts for 5% of all asteroids.
The Koronis family consists of 300 known asteroids which are thought to have been formed at least two billion years ago by a collision. The largest known, 208 Lacrimosa, is about 41 km (25 mi) in diameter, while an additional 20 more have been found that are larger than 25 km in diameter.
The Eos (or Eoan) family is a prominent family of asteroids that orbit the Sun at a distance of 2.96 – 3.03 AUs, and are believed to have formed from a collision 1-2 billion years ago. It consists of 4,400 known members that resemble the S-type asteroid category. However, the examination of Eos and other family members in the infrared show some differences with the S-type, thus why they have their own category (K-type asteroids).
The Themis asteroid family is found in the outer portion of the asteroid belt, at a mean distance of 3.13 AU from the Sun. This core group includes the asteroid 24 Themis (for which it is named) and is one of the more populous asteroid families. It is made up of C-type asteroids with a composition believed to be similar to that of carbonaceous chondrites and consists of a well-defined core of larger asteroids and a surrounding region of smaller ones.
The largest asteroid to be a true member of a family is 4 Vesta. The Vesta family is believed to have formed as the result of a crater-forming impact on Vesta. Likewise, the HED meteorites may also have originated from Vesta as a result of this collision.
Along with the asteroid bodies, the asteroid belt also contains bands of dust with particle radii of up to a few hundred micrometers. This fine material is produced, at least in part, from collisions between asteroids, and by the impact of micrometeorites upon the asteroids. Three prominent bands of dust have been found within the asteroid belt – which have similar orbital inclinations as the Eos, Koronis, and Themis asteroid families – and so are possibly associated with those groupings.
Originally, the Asteroid Belt was thought to be the remnants of a much larger planet that occupied the region between the orbits of Mars and Jupiter. This theory was originally suggested by Heinrich Olbders to William Herschel as a possible explanation for the existence of Ceres and Pallas. However, this hypothesis has since fallen out of favor for a number of reasons.
First, there is the amount of energy it would have required to destroy a planet, which would have been staggering. Second, there is the fact that the entire mass of the Belt is only 4% that of the Moon. Third, the significant chemical differences between the asteroids do not point towards them having been once part of a single planet.
Today, the scientific consensus is that, rather than fragmenting from a progenitor planet, the asteroids are remnants from the early Solar System that never formed a planet at all. During the first few million years of the Solar System’s history, when gravitational accretion led to the formation of the planets, clumps of matter in an accretion disc coalesced to form planetesimals. These, in turn, came together to form planets.
However, within the region of the Asteroid Belt, planetesimals were too strongly perturbed by Jupiter’s gravity to form a planet. These objects would continue to orbit the Sun as before, occasionally colliding and producing smaller fragments and dust.
During the early history of the Solar System, the asteroids also melted to some degree, allowing elements within them to be partially or completely differentiated by mass. However, this period would have been necessarily brief due to their relatively small size, and likely ended about 4.5 billion years ago, in the first tens of millions of years of the Solar System’s formation.
Though they are dated to the early history of the Solar System, the asteroids (as they are today) are not samples of its primordial self. They have undergone considerable evolution since their formation, including internal heating, surface melting from impacts, space weathering from radiation, and bombardment by micrometeorites. Hence, the Asteroid Belt today is believed to contain only a small fraction of the mass of the primordial belt.
Computer simulations suggest that the original asteroid belt may have contained as much mass as Earth. Primarily because of gravitational perturbations, most of the material was ejected from the belt a million years after its formation, leaving behind less than 0.1% of the original mass. Since then, the size distribution of the asteroid belt is believed to have remained relatively stable.
When the asteroid belt was first formed, the temperatures at a distance of 2.7 AU from the Sun formed a “snow line” below the freezing point of water. Essentially, planetesimals formed beyond this radius were able to accumulate ice, some of which may have provided a water source of Earth’s oceans (even more so than comets).
The asteroid belt is so thinly populated that several unmanned spacecraft have been able to move through it; either as part of a long-range mission to the outer Solar System, or (in recent years) as a mission to study larger Asteroid Belt objects. In fact, due to the low density of materials within the Belt, the odds of a probe running into an asteroid are now estimated at less than one in a billion.
The first spacecraft to make a journey through the asteroid belt was the Pioneer 10 spacecraft, which entered the region on July 16th, 1972. As part of a mission to Jupiter, the craft successfully navigated through the Belt and conducted a flyby of Jupiter (which culminated in December of 1973) before becoming the first spacecraft to achieve escape velocity from the Solar System.
For the most part, these missions were part of missions to the outer Solar System, where opportunities to photograph and study asteroids were brief. Only the Dawn, NEAR and JAXA’s Hayabusamissions have studied asteroids for a protracted period in orbit and at the surface. Dawn explored Vesta from July 2011 to September 2012 and is currently orbiting Ceres (and sending back many interesting pictures of its surface features).
And someday, if all goes well, humanity might even be in a position to begin mining the asteroid belt for resources – such as precious metals, minerals, and volatiles. These resources could be mined from an asteroid and then used in space of in-situ utilization (i.e. turning them into construction materials and rocket propellant), or brought back to Earth.
It is even possible that humanity might one day colonize larger asteroids and establish outposts throughout the Belt. In the meantime, there’s still plenty of exploring left to do, and quite possibly millions of more objects out there to study.
Sequence of OSIRIS narrow-angle camera images from 12 August 2015, just a few hours before the comet reached perihelion. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
See hi res images below[/caption]
A spectacular display of celestial fireworks like none ever witnessed before, burst forth from Rosetta’s comet right on time – commemorating the Europeans spacecraft’s history making perihelion passage after a year long wait of mounting excitement and breathtaking science.
And the perihelion passage did not disappoint – living up to its advance billing by spewing forth an unmatched display of otherworldly outbursts of gas jets and dust particles due to surface heating from the warming effects of the sun as the comet edged ever closer, coming within 186 million kilometers of mighty Sol.
ESA has released a brand new series of images, shown above and below, documenting sparks flying – as seen by Rosetta’s OSIRIS narrow-angle camera and NAVCAM wider angle cameras on August 12 and 13 – just a few hours before the rubby ducky shaped comet reached perihelion along its 6.5-year orbit around the sun.
Indeed the navcam camera image below was taken just an hour before the moment of perihelion, at 01:04 GMT, from a distance of around 327 kilometers!
Frozen ices are seen blasting away from the comet in a hail of gas and dust particles as rising solar radiation heats the nucleus and fortifies the comet’s atmosphere, or coma, and its tail.
After a decade long chase of over 6.4 billion kilometers (4 Billion miles), ESA’s Rosetta spacecraft arrived at the pockmarked Comet 67P/Churyumov-Gerasimenko exactly a year ago on Aug. 6, 2014 for history’s first ever attempt to orbit a comet for long term study.
In the interim, Rosetta also deployed the piggybacked Philae lander for history’s first landing on a comet on Nov. 12, 2014.
In fact, measurements from Rosetta’s science instruments confirm the comet is belching a thousand times more water vapor today than was observed during Rosetta’s arrival a year ago. It’s spewing some 300 kg of water vapour every second now, compared to just 300 g per second upon arrival. That equates to two bathtubs per second now in Aug. 2015 vs. two small glasses of water per second in Aug. 2014.
Besides gas, 1000 kg of dust per second is simultaneously erupting from the nucleus, “creating dangerous working conditions for Rosetta,” says ESA.
“In recent days, we have been forced to move even further away from the comet. We’re currently at a distance of between 325 km and 340 km this week, in a region where Rosetta’s startrackers can operate without being confused by excessive dust levels – without them working properly, Rosetta can’t position itself in space,” comments Sylvain Lodiot, ESA’s spacecraft operations manager, in an ESA statement.
Here’s an OSIRIS image taken just hours prior to perihelion, that’s included in the lead animation of this story.
The period of the comet’s peak intensity, as seen in all these images, is expected to continue past perihelion for several weeks at least and fulfils the dreams of a scientific goldmine for all the research teams and hundreds of researchers involved with Rosetta and Philae.
“Activity will remain high like this for many weeks, and we’re certainly looking forward to seeing how many more jets and outburst events we catch in the act, as we have already witnessed in the last few weeks,” says Nicolas Altobelli, acting Rosetta project scientist.
And Rosetta still has lots of fuel, and just as important – funding – to plus up its ground breaking science discoveries.
ESA recently granted Rosetta a 9 month mission extension to continue its research activities as well as having been given the chance to accomplish one final and daring historic challenge.
Engineers will attempt to boldly go and land the probe on the undulating surface of the comet.
Officials with the European Space Agency (ESA) gave the “GO” on June 23 saying “The adventure continues” for Rosetta to march forward with mission operations until the end of September 2016.
If all continues to go well “the spacecraft will most likely be landed on the surface of Comet 67P/Churyumov-Gerasimenko” said ESA.
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.