Posted on by Matt Williams

How Long Does it Take to get to the Asteroid Belt?

It's long been thought that a giant asteroid, which broke up long ago in the main asteroid belt between Mars and Jupiter, eventually made its way to Earth and led to the extinction of the dinosaurs. New studies say that the dinosaurs may have been facing extinction before the asteroid strike, and that mammals were already on the rise. Image credit: NASA/JPL-Caltech

Between the orbits of Mars and Jupiter lies the Solar System’s Main Asteroid Belt. Consisting of millions of objects that range in size from hundreds of kilometers in diameter (like Ceres and Vesta) to one kilometer or more, the Asteroid Belt has long been a source of fascination for astronomers. Initially, they wondered why the many objects that make it up did not come together to form a planet. But more recently, human beings have been eyeing the Asteroid Belt for other purposes.

Whereas most of our efforts are focused on research – in the hopes of shedding additional light on the history of the Solar System – others are looking to tap for its considerable wealth. With enough resources to last us indefinitely, there are many who want to begin mining it as soon as possible. Because of this, knowing exactly how long it would take for spaceships to get there and back is becoming a priority.

Distance from Earth:

The distance between the Asteroid Belt and Earth varies considerably depending on where we measure to. Based on its average distance from the Sun, the distance between Earth and the edge of the Belt that is closest to it can be said to be between 1.2 to 2.2 AUs, or 179.5 and 329 million km (111.5 and 204.43 million mi).

The asteroids of the inner Solar System and Jupiter: The donut-shaped asteroid belt is located between the orbits of Jupiter and Mars. Credit: Wikipedia Commons
The asteroids of the inner Solar System and Jupiter: The donut-shaped asteroid belt is located between the orbits of Jupiter and Mars. Credit: Wikipedia Commons

However, at any given time, part of the Asteroid Belt will be on the opposite side of the Sun, relative to Earth. From this vantage point, the distance between Earth and the Asteroid Blt ranges from 3.2 and 4.2 AU – 478.7 to 628.3 million km (297.45 to 390.4 million mi). To put that in perspective, the distance between Earth and the Asteroid Belt ranges between being slightly more than the distance between the Earth and the Sun (1 AU), to being the same as the distance between Earth and Jupiter (4.2 AU) when they are at their closest.

But of course, for reasons of fuel economy and time, asteroid miners and exploration missions are not about to take the long way! As such, we can safely assume that the distance between Earth and the Asteroid Belt when they are at their closest is the only measurement worth considering.

Past Missions:

The Asteroid Belt is so thinly populated that several unmanned spacecraft have been able to move through it on their way to the outer Solar System. In more recent years, missions to study larger Asteroid Belt objects have also used this to their advantage, navigating between the smaller objects to rendezvous with bodies like Ceres and Vesta. 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 (a journey of 135 days). As part of its mission to Jupiter, the craft successfully navigated through the Belt and conducted a flyby of Jupiter (in December of 1973) before becoming the first spacecraft to achieve escape velocity from the Solar System.

An artist's illustration of NASA's Dawn spacecraft approaching Ceres. Image: NASA/JPL-Caltech.
An artist’s illustration of NASA’s Dawn spacecraft approaching Ceres. Image: NASA/JPL-Caltech.

At the time, there were concerns that the debris would pose a hazard to the Pioneer 10 space probe. But since that mission, 11 additional spacecraft have passed through the Asteroid Belt without incident. These included Pioneer 11, Voyager 1 and 2, Ulysses, Galileo, NEAR, Cassini, Stardust, New Horizons, the ESA’s Rosetta, and most recently, the Dawn spacecraft.

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 Hayabusa missions 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 gravity data on the dwarf planet’s gravity) and is expected to remain there until 2017.

Fastest Mission to Date:

The fastest mission humanity has ever mounted was the New Horizons mission, which was launched from Earth on Jan. 19th, 2006. The mission began with a speedy launch aboard an Atlas V rocket, which accelerated it to a a speed of about 16.26 km per second (58,536 km/h; 36,373 mph). At this speed, the probe reached the Asteroid Belt by the following summer, and made a close approach to the tiny asteroid 132524 APL by June 13th, 2006 (145 days after launching).

However, even this pales in comparison to Voyager 1, which was launched on Sept. 5th, 1977 and reached the Asteroid Belt on Dec. 10th, 1977 – a total of 96 days. And then there was the Voyager 2 probe, which launched 15 days after Voyager 1 (on Sept. 20th), but still managed to arrive on the same date – which works out to a total travel time of 81 days.

For Voyager 2, out on the edge of our Solar system, conventional navigation methods don't work too well. Credit: NASA
For Voyager 2, out on the edge of our Solar system, conventional navigation methods don’t work too well. Credit: NASA

Not bad as travel times go. At these speed, a spacecraft could make the trip to the Asteroid Belt, spend several weeks conducting research (or extracting ore), and then make it home in just over six months time. However, one has to take into account that in all these cases, the mission teams did not decelerate the probes to make a rendezvous with any asteroids.

Ergo, a mission to the Asteroid Belt would take longer as the craft would have to slow down to achieve orbital velocity. And they would also need some powerful engines of their own in order to make the trip home. This would drastically alter the size and weight of the spacecraft, which would inevitably mean it would be bigger, slower and a heck of a lot more expensive than anything we’ve sent so far.

Another possibility would be to use ionic propulsion (which is much more fuel efficient) and pick up a gravity assist by conducting a flyby of Mars – which is precisely what the Dawn mission did. However, even with a boost from Mars’ gravity, the Dawn mission still took over three years to reach the asteroid Vesta – launching on Sept. 27th, 2007, and arriving on July 16th, 2011, (a total of 3 years, 9 months, and 19 days). Not exactly good turnaround!

Proposed Future Methods:

A number of possibilities exist that could drastically reduce both travel time and fuel consumption to the Asteroid Belt, many of which are currently being considered for a number of different mission proposals. One possibility is to use spacecraft equipped with nuclear engines, a concept which NASA has been exploring for decades.

The Crew Transfer Vehicle (CTV) using its nuclear-thermal rocket engines to slow down and establish orbit around Mars. Credit: NASA
The Crew Transfer Vehicle (CTV) using its nuclear-thermal rocket engines to slow down and establish orbit around Mars. Credit: NASA

In a Nuclear Thermal Propulsion (NTP) rocket, uranium or deuterium reactions are used to heat liquid hydrogen inside a reactor, turning it into ionized hydrogen gas (plasma), which is then channeled through a rocket nozzle to generate thrust. A Nuclear Electric Propulsion (NEP) rocket involves the same basic reactor converting its heat and energy into electrical energy, which would then power an electrical engine.

In both cases, the rocket would rely on nuclear fission or fusion to generates propulsion rather than chemical propellants, which has been the mainstay of NASA and all other space agencies to date. According to NASA estimates, the most sophisticated NTP concept would have a maximum specific impulse of 5000 seconds (50 kN·s/kg).

Using this engine, NASA scientists estimate that it would take a spaceship only 90 days to get to Mars when the planet was at “opposition” – i.e. as close as 55,000,000 km from Earth. Adjusted for a distance of 1.2 AUs, that means that a ship equipped with a NTP/NEC propulsion system could make the trip in about 293 days (about nine months and three weeks). A little slow, but not bad considering the technology exists.

Another proposed method of interstellar travel comes in the form of the Radio Frequency (RF) Resonant Cavity Thruster, also known as the EM Drive. Originally proposed in 2001 by Roger K. Shawyer, a UK scientist who started Satellite Propulsion Research Ltd (SPR) to bring it to fruition, this drive is built around the idea that electromagnetic microwave cavities can allow for the direct conversion of electrical energy to thrust.

Artist's concept of an interstellar craft equipped with an EM Drive. Credit:
Artist’s concept of an interstellar craft equipped with an EM Drive. Credit: NASA Spaceflight Center

According to calculations based on the NASA prototype (which yielded a power estimate of 0.4 N/kilowatt), a spacecraft equipped with the EM drive could make the trip to Mars in just ten days. Adjusted for a trip to the Asteroid Belt, so a spacecraft equipped with an EM drive would take an estimated 32.5 days to reach the Asteroid Belt.

Impressive, yes? But of course, that is based on a concept that has yet to be proven. So let’s turn to yet another radical proposal, which is to use ships equipped with an antimatter engine. Created in particle accelerators, antimatter is the most dense fuel you could possibly use. When atoms of matter meet atoms of antimatter, they annihilate each other, releasing an incredible amount of energy in the process.

According to the NASA Institute for Advanced Concepts (NIAC), which is researching the technology, it would take just 10 milligrams of antimatter to propel a human mission to Mars in 45 days. Based on this estimate, a craft equipped with an antimatter engine and roughly twice as much fuel could make the trip to the Asteroid Belt in roughly 147 days. But of course, the sheer cost of creating antimatter – combined with the fact that an engine based on these principles is still theoretical at this point – makes it a distant prospect.

Basically, getting to the Asteroid Belt takes quite a bit of time, at least when it comes to the concepts we currently have available. Using theoretical propulsion concepts, we are able to cut down on the travel time, but it will take some time (and lots of money) before those concepts are a reality. However, compared to many other proposed missions – such as to Europa and Enceladus – the travel time is shorter, and the dividends quite clear.

As already stated, there are enough resources – in the form of minerals and volatiles – in the Asteroid Belt to last us indefinitely. And, should we someday find a way to cost-effective way to send spacecraft there rapidly, we could tap that wealth and begin to usher in an age of post-scarcity! But as with so many other proposals and mission concepts, it looks like we’ll have to wait for the time being.

We have written many articles about the asteroid belt for Universe Today. Here’s Where Do Asteroids Come From?, Why the Asteroid Belt Doesn’t Threaten Spacecraft, and Why isn’t the Asteroid Belt a Planet?.

Also, be sure to learn which is the Largest Asteroid in the Solar System, and about the asteroid named after Leonard Nimoy. And here’s 10 Interesting Facts about Asteroids.

We also have many interesting articles about the Dawn spacecraft’s mission to Vesta and Ceres, and asteroid mining.

To learn more, check out NASA’s Lunar and Planetary Science Page on asteroids, and the Hubblesite’s News Releases about Asteroids.

Astronomy Cast also some interesting episodes about asteroids, like Episode 55: The Asteroid Belt and Episode 29: Asteroids Make Bad Neighbors.

Sources:

Posted on by Matt Williams

How Far is the Asteroid Belt from Earth?

Artist's impression of the asteroid belt. Image credit: NASA/JPL-Caltech

In the 18th century, observations made of all the known planets (Mercury, Venus, Earth, Mars, Jupiter and Saturn) led astronomers to the realization that there was a pattern in their orbits. Eventually, this led to the Titius–Bode law, which predicted the amount of space that naturally existed between each celestial body that orbited our Sun. In accordance with this law, astronomers noted that there appeared to be a discernible gap between the orbits of Mars and Jupiter.

Investigations into this gap eventually resulted in astronomers observing several bodies of various size. This led to the creation of the term “asteroid” (Greek for ‘star-like’ or ‘star-shaped’), as well as “Asteroid Belt”, once it became clear just how many there were. Through various methods, astronomers have since confirmed the existence of several million objects between the orbit of Mars and Jupiter. They have also determined, with a certain degree of accuracy, how far it is from our planet.

Structure and Composition:

The Asteroid Belt consists of several large bodies, coupled with millions of smaller size. The larger bodies, such as Ceres, Vesta, Pallas, and Hygiea, account for half of the belt’s total mass, with almost one-third accounted for by Ceres alone. Beyond that, over 200 asteroids that are larger than 100 km in diameter, and 0.7–1.7 million asteroids with a diameter of 1 km or more.

The asteroids of the inner Solar System and Jupiter: The donut-shaped asteroid belt is located between the orbits of Jupiter and Mars. Credit: Wikipedia Commons
The asteroids of the inner Solar System and Jupiter: The donut-shaped asteroid belt is located between the orbits of Jupiter and Mars. Credit: Wikipedia Commons

It total, the Asteroid Belt’s mass is estimated to be 2.8×1021 to 3.2×1021 kilograms – which is equivalent to about 4% of the Moon’s mass. While most asteroids are composed of rock, a small portion of them contain 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.

Despite the impressive number of objects contained within the belt, the Main Belt’s asteroids are also spread over a very large volume of space. As a result, the average distance between objects is roughly 965,600 km (600,000 miles), meaning that the Main Belt consists largely of empty space. 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 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 gaps are similar to what is seen with Saturn’s and other gas giants’ systems of rings.

Orbit Around the Sun:

Located between Mars and Jupiter, the belt ranges in distance between 2.2 and 3.2 astronomical units (AU) from the Sun – 329 million to 478.7 million km (204.43 million to 297.45 million mi). It is also an estimated 1 AU thick (149.6 million km, or 93 million mi), meaning that it occupies the same amount of distance as what lies between the Earth to the Sun.

The distance of an asteroid from the Sun (its semi-major axis) depends upon its distribution into one of three different zones based on the Belt’s “Kirkwood Gaps”. Zone I lies between the 4:1 resonance and 3:1 resonance Kirkwood gaps, which are roughly 2.06 and 2.5 AUs (3 to 3.74 billion km; 1.86 to 2.3 billion mi) 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 (4.22 billion km; 2.6 mi) from the Sun. Zone III, the outermost section of the Belt, extends from the outer edge of Zone II to the 2:1 resonance gap, located some 3.28 AU (4.9 billion km; 3 billion mi) from the Sun.

Distance from Earth:

The distance between the Asteroid Belt and Earth varies considerably depending on where we measure to. Based on its average distance from the Sun, the distance between Earth and the closest edge of the Belt can be said to be between 1.2 to 2.2 AUs, or 179.5 and 329 million km (111.5 and 204.43 million mi). But of course, at any given time, part of the Asteroid Belt will be on the opposite side of the Sun relative to us as well.

From this vantage point, the distance between Earth and the Asteroid Belt ranges from 3.2 and 4.2 AU – 478.7 to 628.3 million km (297.45 to 390.4 million mi). To put that in perspective, the distance between Earth and the Asteroid Belt ranges from being slightly more than the distance between the Earth and the Sun (1 AU), to being the same as the distance between Earth and Jupiter (4.2 AU) when they are at their closest.

Naturally, any exploration or other kind of mission launched from Earth is going to take the shortest route, unless it is aiming for a specific asteroid. And even then, mission planners will time the launch to ensure that we are closest to the destination. Hence, we can safely use the estimates of 1.2 – 2.2 AU to gauge the distance between us and the Main Belt.

Even so, at its closest, getting to the Asteroid Belt would involve a bit of a hike! In short, it is approximately 179.5 million km (or 111.5 million mi) distant from us at any given time. As such, knowing just how much time and energy it would take to get their and back is going to come in handy if and when we begin mounting crewed missions to the Belt, not to mention the prospect of asteroid mining!

We have written many interesting articles on the Asteroid  Belt here at Universe Today. Here’s What is the Asteroid Belt?, Where Do Asteroids Come From?, Why the Asteroid Belt Doesn’t Threaten Spacecraft, Why isn’t the Asteroid Belt a Planet?, and 10 Interesting Facts about Asteroids.

To learn more, check out NASA’s Lunar and Planetary Science Page on asteroids, and the Hubblesite’s News Releases about Asteroids.

Astronomy Cast also some interesting episodes about asteroids, like Episode 55: The Asteroid Belt and Episode 29: Asteroids Make Bad Neighbors.

Sources:

Posted on by Nancy Atkinson

The Moon’s Mare Imbrium Was Hit By Protoplanetary Size Impactor

A photo of the full moon, taken from Apollo 11 on its way home to Earth, from about 18,520 km (10,000 nm) away. Credit: NASA
A photo of the full moon, taken from Apollo 11 on its way home to Earth, from about 18,520 km (10,000 nm) away. Credit: NASA

The asteroid that punched an “eye” in the Moon is about 10 times more massive than originally thought. Researchers say a protoplanet-sized body slammed into the Moon about 3.8 billion years ago, creating the area called Imbrium Basin that forms the right eye of the so-called “Man in the Moon.” Additionally, this large body also indicates that protoplanet-sized asteroids may have been common in the early solar system, putting the “heavy” into the Late Heavy Bombardment.

“We show that Imbrium was likely formed by an absolutely enormous object, large enough to be classified as a protoplanet,” said Pete Schultz from Brown University. “This is the first estimate for the Imbrium impactor’s size that is based largely on the geological features we see on the Moon.”

Mare Imbrium or the Sea of Showers is highlighted in this map of the moon. The other large, dark spots are also basins created from asteroid impacts. Credit: NASA
Mare Imbrium or the Sea of Showers is highlighted in this map of the moon. The other large, dark spots are also basins created from asteroid impacts. Credit: NASA

The Imbrium Basin is easily seen when the Moon is full, as a dark patch in the Moon’s northwestern quadrant. It is about 750 miles across, and a closer look shows the basin is surrounded by grooves and gashes that radiate out from the center of the basin, plus a second set of grooves with a different alignment that have puzzled astronomers for decades.

To re-enact the impact, Schultz used the Vertical Gun Range at the NASA Ames Research Center to conduct hypervelocity impact experiments. This facility has a 14-foot cannon that fires small projectiles at up to 25,750 km/hr (16,000 miles per hour), and high-speed cameras record the ballistic dynamics. During his experiments, Schultz noticed that in addition to the usual crater ejecta from the impact, the impactors themselves – if large enough — had a tendency to break apart when they first made contact with the surface. Then these chunks would continue to travel at a high speeds, skimming along and plowing across the surface, creating grooves and gouges.

Grooves and gashes associated with the Imbrium Basin on the Moon have long been puzzling. New research shows how some of these features were formed and uses them to estimate the size of the Imbrium impactor. The study suggests it was big enough to be considered a protoplanet. NASA/Northeast Planetary Data Center/Brown University
Grooves and gashes associated with the Imbrium Basin on the Moon have long been puzzling. New research shows how some of these features were formed and uses them to estimate the size of the Imbrium impactor. The study suggests it was big enough to be considered a protoplanet. NASA/Northeast Planetary Data Center/Brown University

The results showed the second set of grooves were likely formed by these large chunks of the impactor that sheared off on initial contact with the surface.

“The key point is that the grooves made by these chunks aren’t radial to the crater,” Schultz said in a press release. “They come from the region of first contact. We see the same thing in our experiments that we see on the Moon — grooves pointing up-range, rather than the crater.”

The second set of groove trajectories could be used to estimate the impactor’s size. Schultz worked with David Crawford of the Sandia National Laboratories to generate computer models of the physics of various sizes of impactors, and they were able to estimate the impactor that created Imbrium Basin to be more than 250 km (150 miles) across, which is two times larger in diameter and 10 times more massive than previous estimates. This puts the impactor in the range of being the size of a protoplanet.

“That’s actually a low-end estimate,” Schultz said. “It’s possible that it could have been as large as 300 kilometers.”
Previous estimates, Schultz said, were based solely on computer models and yielded a size estimate of only about 50 miles in diameter.

Schultz and his colleagues also used the same methods to estimate the sizes of impactors related to several other basins on the Moon, for example, the Moscoviense and Orientale basins on the Moon’s far side, which yielded impactor sizes of 100 and 110 kilometers across respectively, larger than some previous estimates.

Combining these new estimates with the fact that there are even larger impact basins on the Moon and other planets, Schultz concluded that protoplanet-sized asteroids may have been common in the early solar system, and he called them the “lost giants” of the Late Heavy Bombardment, a period of intense comet and asteroid bombardment thought to have pummeled the Moon and all the planets including the Earth about 4 to 3.8 billion years ago.

“The Moon still holds clues that can affect our interpretation of the entire solar system,” he said. “Its scarred face can tell us quite a lot about what was happening in our neighborhood 3.8 billion years ago.”

Schultz’s study was published in Nature.

Source: Brown University

Posted on by Evan Gough

Returned Samples Of Asteroid Itokawa Show Violent 4.5 Billion Year History

The surface patterns on one of the microscopic dust particles from asteroid Itokawa. Image: JAXA
The surface patterns on one of the microscopic dust particles from asteroid Itokawa. Image: JAXA

In 2003, the Japanese Aerospace Exploration Agency (JAXA) launched the Hayabusa probe. Its mission was to rendezvous with asteroid 25143 Itokawa in 2005. Once there, it studied a number of things about Itokawa, including its shape, topography, composition, colour, spin, density, and history. But the most exciting part of its mission was to collect samples from the asteroid and return them to Earth.

The mission suffered some complications, including the failure of Minerva, Hayabusa’s detachable mini-lander. But Hayabusa did land on the asteroid, and it did collect some samples; tiny grains of material from the surface of Itokawa. This was the first time a mission had landed somewhere and returned samples, other than missions to the Moon.

The Hayabusa spacecraft burned up on re-entry into Earth's atmosphere, but the capsule containing the samples survived. The glowing piece on the bottom front of the debris stream is the sample capsule. Image: NASA Ames, Public Domain
The Hayabusa spacecraft burned up on re-entry into Earth’s atmosphere, but the capsule containing the samples survived. The glowing piece on the bottom front of the debris stream is the sample capsule. Image: NASA Ames, Public Domain

Once the collected grains made it back to Earth in 2010, and were confirmed to be from the asteroid, scientists got excited. These grains would be key to helping understand the early Solar System when the planetary bodies were formed. And they have revealed a sometimes violent history going back 4.5 billion years.

The grains themselves are truly microscopic, at just over 10 micrometers in size. The marks and surface patterns on them are measured in nanometers. Initially, all the marks on the surfaces of the particles were thought to be of one type. But the team behind the study used electron microscopes and X-Ray Microtomography to reveal four different types of patterns on their surfaces.

One 4.5 billion year old pattern shows crystallization from intense heat. At this time period, Itokawa was part of a larger asteroid. The second pattern indicates a collision with a meteor about 1.3 billion years ago. Another pattern was formed by exposure to the solar wind between 1 million and 1,000 years ago. A fourth pattern detected by scientists shows that the particles have been rubbing against each other.

The team has concluded that Itokawa didn’t always exist in its current shape and form. When it was formed over 4 billion years ago, it was about 40 times bigger than it is now. That parent body was destroyed, and the researchers think that Itokawa re-formed from fragments of the parent body.

If there is still any lingering doubt about the violent nature of the Solar System’s history, the grains from Itokawa help dispel it. Collision, fragmentation, bombardments, and of course solar wind, seem to be the norm in our Solar System’s history.

The return of these samples was a bit of a happy accident. The sample collection mechanism on Hayabusa suffered a failure, and the returned dust grains were actually kicked up by the landing of the probe, and some ended up in the sample capsule.

For their part, JAXA has already launched Hayabusa’s successor, Hayabusa 2. It was launched in December 2014, and is headed for asteroid 162173 Ryugu. It should reach its destination in July 2018, and spend a year and a half there. Hayabusa 2 is also designed to collect asteroid samples and return them to Earth, this time using an explosive device to dig into the asteroid’s surface for a sample. Hayabusa 2 should return to Earth in December 2020.

An artist's image of Hayabusa leaving Earth. Image credit: JAXA
An artist’s image of Hayabusa leaving Earth. Image credit: JAXA

Hayabusa suffered several failures, including the failure of its mini-lander, problems with sample collection, and it even suffered damaged to its solar panels caused by a solar flare, which reduced its power and delayed its arrival at Itokawa. Yet it still ended up being a success in the end.

If Hayabusa 2 can avoid some of these problems, who knows what we may learn from more intentional samples. Sample missions are tricky and complex. If Hayabusa can return samples, it would be only the fourth body to have samples successfully returned to Earth, including the Moon, asteroid Itokawa, and comet Wild 2.

Posted on by Matt Williams

Centaurs Keep Their Rings From Greedy Gas Giants

Artist's impression of what the rings of the asteroid Chariklo would look like from the small body's surface. The rings' discovery was a first for an asteroid. Credit: ESO/L. Calçada/Nick Risinger (skysurvey.org)

When we think of ring systems, what naturally comes to mind are planets like Saturn. It’s beautiful rings are certainly the most well known, but they are not the only planet in our Solar System to have them. As the Voyager missions demonstrated, every planet in the outer Solar System – from Jupiter to Neptune – has its own system of rings. And in recent years, astronomers have discovered that even certain minor planets – like the Centaur asteroids 10199 Chariklo and 2006 Chiron – have them too.

This was a rather surprising find, since these objects have such chaotic orbits. Given that their paths through the Solar System are frequently altered by the powerful gravity of gas giants, astronomers have naturally wondered how a minor planet could retain a system of rings. But thanks to a team of researchers from the Sao Paulo State University in Brazil, we may be close to answering that question.

In a study titled “The Rings of Chariklo Under Close Encounters With The Giant Planets“, which appeared recently in The Astrophysical Journal, they explained how they constructed a model of the Solar System that incorporated 729 simulated objects. All of these objects were the same size as Chariklo and had their own system of rings. They then went about the process of examining how interacting with gas giant effected them.

Artist's impression of rings around the asteroid Chariklo. This was the first asteroid where rings were discovered. Credit: ESO/L. Calçada/M. Kornmesser/Nick Risinger (skysurvey.org)
Artist’s impression of rings around the Centaur Chariklo, the first asteroid where rings were discovered. Credit: ESO/L. Calçada/M. Kornmesser/Nick Risinger (skysurvey.org)

To break it down, Centaurs are a population of objects within our Solar System that behave as both comets and asteroids (hence why they are named after the hybrid beasts of Greek mythology). 10199 Chariklo is the largest known member of the Centaur population, a possible former Trans-Neptunian Object (TNO) which currently orbits between Saturn and Uranus.

The rings around this asteroid were first noticed in 2013 when the asteroid underwent a stellar occultation. This revealed a system of two rings, with a radius of 391 and 405 km and widths of about 7 km 3 km, respectively. The absorption features of the rings showed that they were partially composed of water ice. In this respect, they were much like the rings of Jupiter, Saturn, Uranus and the other gas giants, which are composed largely of water ice and dust.

This was followed by findings made in 2015 that indicated that 2006 Chiron – another major Centaur – could have a ring of its own. This led to further speculation that there might be many minor planets in our Solar System that have a system of rings. Naturally, this was a bit perplexing to astronomers, since rings are fragile structures that were thought to be exclusive to the gas giants of our System.

As Professor Othon Winter, the lead researcher of the Sao Paulo team, told Universe Today via email:

“At first it was a surprise to find a Centaur with rings, since the Centaurs have chaotic orbits wandering between the giant planets and having frequent close encounters with them. However, we have shown that in most of the cases the ring system can survive all the close encounters with the giant planets. Therefore,  Centaurs with rings might be much more common than we thought before.”

Arist's impression of Chiron and its possible ring. Credit: dailygalaxy.com
Artist’s impression of Chiron, showing a possible ring system. Credit: dailygalaxy.com

For the sake of their study, Winter and his colleagues considered the orbits of 729 simulated clones of Chariklo as they orbited the Sun over the course of 100 million years. From this, Winter and his colleagues found that each Centaur averaged about 150 close encounters with a gas giant, within one Hill radius of the planet in question. As Winter described it:

“The study was made in two steps. First we considered a set of more than 700 clones of Chariklo. The clones had initial trajectories that were slightly different from Chariklo for statistical purposes (since we are dealing with chaotic trajectories) and computationally simulated their orbital evolution forward in time (to see their future) and also backward in time (to see their past). During these simulations we archived the information of all the close encounters (many thousands) they had with each of the giant planets.”

“In the second step, we performed simulations of each one of the close encounters found in the first step, but now including a disk of particles around Chariklo  (representing the ring particles). Then, at the end of each simulation we analyzed what happened to the particles. Which ones were removed from Chariklo  (escaping its gravitational field)? Which ones were strongly disturbed (still orbiting around Chariklo)? Which ones did not suffer any significant effect?”

In the end, the simulations showed that in 90 percent of the cases, the rings of the Centaurs survived their close encounters with gas giants, whereas they were disturbed in 4 percent of cases, and were stripped away only 3 percent of the time. Thus, they concluded that if there is an efficient mechanism that creates the rings, then it is strong enough to let Centaurs keep them.

Due to their dual nature, astronomers refer to asteroids that behave as both comets and asteroids as Centaurs. Credit: jpl.nasa.gov
Due to their dual nature, the name Centaur has stuck when referring to objects that act as both comets and asteroids. Credit: jpl.nasa.gov

More than that, their research would seem to indicate that what was considered unique to certain planetary bodies may actually be more commonplace. “It reveals that our Solar System is complex not just as whole or for large bodies,” said Winter, “but even small bodies may show complex structures and even more complex temporal evolution.”

The next step for the research team is to study ring formation, which could show that they in fact picking them up from the gas giants themselves. But regardless of where they come from, its becoming increasingly clear that Centaurs like 10199 Chariklo are not alone. What’s more, they aren’t giving up their rings anytime soon!

Further Reading: iopscience.iop.org

Posted on by Evan Gough

Earth Has An Almost-Moon

Earth has a new quasi-moon: an asteroid called 2016 H03. (Not shown) Image: NASA
Earth has a new quasi-moon: an asteroid called 2016 H03. (Not shown) Image: NASA

Earth has a small companion that NASA is calling an almost-Moon. The small asteroid, called 2016 H03, isn’t quite a moon because it’s actually orbiting the Sun. In its orbit around the Sun, it spends about half of its time closer to the Sun than the Earth.

2016 H03 is called a “quasi-moon” or a “near-Earth companion”. It doesn’t quite qualify as a moon because of its orbit.

Paul Chodas is the manager of NASA’s Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California. He had this to say about 2016 H03: “Since 2016 HO3 loops around our planet, but never ventures very far away as we both go around the sun, we refer to it as a quasi-satellite of Earth.”

2016 H03’s orbit is tilted relative to Earth’s, and it passes through the plane of Earth’s orbit. Over the decades, it also performs a slow, back and forth twist. NASA describes 2016 H03’s orbit as a game of leap frog.

“The asteroid’s loops around Earth drift a little ahead or behind from year to year, but when they drift too far forward or backward, Earth’s gravity is just strong enough to reverse the drift and hold onto the asteroid so that it never wanders farther away than about 100 times the distance of the moon,” said Chodas. “The same effect also prevents the asteroid from approaching much closer than about 38 times the distance of the moon. In effect, this small asteroid is caught in a little dance with Earth.”

Earth’s little quasi-moon has been in its stable orbit for about a century, according to calculations, though it was only spotted on April 27th, 2016, by the Pan-STARRS 1 asteroid survey telescope in Hawaii. Pan-STARRS 1 is operated by the University of Hawaii’s Institute for Astronomy and NASA’s Planetary Defense Coordination Office. (Did you know we had a Planetary Defense Coordination Office?)

2016 H03 is small. It’s exact size has not been established, but it’s between 40 and 100 meters (120 and 300 ft.) It’s been around a century, and calculations say it will be around for centuries more.

2016 H03 is not quite unique. Earth has had other dance partners like it.

“One other asteroid — 2003 YN107 — followed a similar orbital pattern for a while over 10 years ago, but it has since departed our vicinity. This new asteroid is much more locked onto us. Our calculations indicate 2016 HO3 has been a stable quasi-satellite of Earth for almost a century, and it will continue to follow this pattern as Earth’s companion for centuries to come,” said Chudas.

NASA tracks thousands of NEOs and assesses their risk of collision with Earth. Though 2016 H03 is an interesting specimen because of its orbit, it poses no threat to Earth.

Posted on by Evan Gough

470 Million Year Old Meteorite Discovered In Swedish Quarry

Osterplana 65, the meteorite at the heart of a mystery. This meteorite is different than the thousands of other meteorites in collections around the world. Image: Birger Schmitz
Osterplana 65, the meteorite at the heart of a mystery. This meteorite is different than the thousands of other meteorites in collections around the world. Image: Birger Schmitz

470 million years ago, somewhere in our Solar System, there was an enormous collision between two asteroids. We know this because of the rain of meteorites that struck Earth at that time. But inside that rain of meteorites, which were all of the same type, there is a mystery: an oddball, different from the rest. And that oddball could tell us something about how rocks from space can change ecosystems, and allow species to thrive.

This oddball meteorite has a name: Osterplana 65. It’s a fossilized meteorite, and it was found in a limestone quarry in Sweden. Osterplana 65 fell to Earth some 470 mya, during the Ordovician period, and sank to the bottom of the ocean. There, it became sequestered in a bed of limestone, itself created by the sea-life of the time.

The Ordovician period is marked by a couple thing: a flourishing of life similar to the Cambrian period that preceded it, and a shower of meteors called the Ordovician meteor event. There is ample evidence of the Ordovician meteor event in the form of meteorites, and they all conform to similar chemistry and structure. So it’s long been understood that they all came from the same parent body.

The collision that caused this rain of meteorites had to have two components, two parent bodies, and Osterplana 65 is evidence that one of these parent bodies was different. In fact, Ost 65 represents a so far unknown type of meteorite.

The faint grey lines in this electron image of Ost 65 are called "shock deformation lamellae" and they are evidence that Ost 65 was the result of a collision. Image: B. Schmidt
The faint grey lines in this electron image of Ost 65 are called “shock deformation lamellae” and they are evidence that Ost 65 was the result of a collision. Image: B. Schmidt

The study that reported this finding was published in Nature on June 14 2016. As the text of the study says, “Although single random meteorites are possible, one has to consider that Öst 65 represents on the order of one per cent of the meteorites that have been found on the mid-Ordovician sea floor. “It goes on to say, “…Öst 65 may represent one of the dominant types of meteorites arriving on Earth 470 Myr ago.”

The discovery of a type of meteorite falling on Earth 470 mya, and no longer falling in our times, is important for a couple reasons. The asteroid that produced it is probably no longer around, and there is no other source for meteorites like Ost 65 today.

The fossil record of a type of meteorite no longer in existence may help us unravel the story of our Solar System. The asteroid belt itself is an ongoing evolution of collision and destruction. It seems reasonable that some types of asteroids that were present in the earlier Solar System are no longer present, and Ost 65 provides evidence that that is true, in at least one case.

Ost 65 shows us that the diversity in the population of meteorites was greater in the past than it is today. And Ost 65 only takes us back 470 mya. Was the population even more diverse even longer ago?

The Earth is largely a conglomeration of space rocks, and we know that there are no remnants of these Earthly building blocks in our collections of meteorites today. What Ost 65 helps prove is that the nature of space rock has changed over time, and the types of rock that came together to form Earth are no longer present in space.

Ost 65 was found in amongst about 100 other meteorites, which were all of the same type. It was found in the garbage dump part of the quarry. It’s presence is a blemish on the floor tiles that are cut at the quarry. Study co-author Birgen Schmitz told the BBC in an interview that “It used to be that they threw away the floor tiles that had ugly black dots in them. The very first fossil meteorite we found was in one of their dumps.”

According to Schmitz, he and his colleagues have asked the quarry to keep an eye out for these types of defects in rocks, in case more of them are fossilized meteorites.

Finding more fossilized meteorites could help answer another question that goes along with the discovery of Ost 65. Did the types and amounts of space rock falling to Earth at different times help shape the evolution of life on Earth? If Ost 65 was a dominant type of meteorite falling to Earth 470 mya, what effect did it have? There appear to be a confounding number of variables that have to be aligned in order for life to appear and flourish. A shower of minerals from space at the right time could very well be one of them.

Whether that question ever gets answered is anybody’s guess at this point. But Ost 65 does tell us one thing for certain. As the text of the study says, “Apparently there is potential to reconstruct important aspects of solar-system history by looking down in Earth’s sediments, in addition to looking up at the skies.”

Posted on by Fraser Cain

Astronomy Cast Ep. 416: Fireballs from Space!

Every now and then we look up and see bright fiery balls falling from the sky. Don’t panic, these are just bolides. Sometimes they leave trails, sometimes they explode, and sometimes they survive all the way to the ground.

Visit the Astronomy Cast Page to subscribe to the audio podcast!

We record Astronomy Cast as a live Google+ Hangout on Air every Monday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch here on Universe Today or from the Astronomy Cast Google+ page.

Posted on by Matt Williams

Scientists Identify the Source of the Moon’s Water

New research finds that asteroids delivered as much 80 percent of the Moon's water. Credit: LPI/David A. Kring

Over the course of the past few decades, our ongoing exploration the Solar System has revealed some surprising discoveries. For example, while we have yet to find life beyond our planet, we have discovered that the elements necessary for life (i.e organic molecules, volatile elements, and water) are a lot more plentiful than previously thought. In the 1960’s, it was theorized that water ice could exist on the Moon; and by the next decade, sample return missions and probes were confirming this.

Since that time, a great deal more water has been discovered, which has led to a debate within the scientific community as to where it all came from. Was it the result of in-situ production, or was it delivered to the surface by water-bearing comets, asteroids and meteorites? According to a recent study produced by a team of scientists from the UK, US and France, the majority of the Moon’s water appears to have come from meteorites that delivered water to Earth and the Moon billions of years ago.

For the sake of their study, which appeared recently in Nature Communications, the international research team examined the samples of lunar rock and soil that were returned by the Apollo missions. When these samples were originally examined upon their return to Earth, it was assumed that the trace of amounts of water they contained were the result of contamination from Earth’s atmosphere since the containers in which the Moon rocks were brought home weren’t airtight. The Moon, it was widely believed, was bone dry.

The blue areas show locations on the Moon's south pole where water ice is likely to exist (NASA/GSFC)
The blue areas show locations on the Moon’s south pole where water ice is likely to exist. Credit: NASA/GSFC

However, a 2008 study revealed that the samples of volcanic glass beads contained water molecules (46 parts per million), as well as various volatile elements (chlorine, fluoride and sulfur) that could not have been the result of contamination. This was followed up by the deployment of the Lunar Reconnaissance Orbiter (LRO) and the Lunar Crater Observation and Sensing Satellite (LCROSS) in 2009, which discovered abundant supplies of water around the southern polar region,

However, that which was discovered on the surface paled in comparison the water that was discovered beneath it. Evidence of water in the interior was first revealed by the ISRO’s Chandrayaan-1 lunar orbiter – which carried the NASA’s Moon Mineralogy Mapper (M3) and delivered it to the surface. Analysis of this and other data has showed that water in the Moon’s interior is up to a million times more abundant than what’s on the surface.

The presence of so much water beneath the surface has begged the question, where did it all come from? Whereas water that exists on the Moon’s surface in lunar regolith appears to be the result of interaction with solar wind, this cannot account for the abundant sources deep underground. A previous study suggested that it came from Earth, as the leading theory for the Moon’s formation is that a large Mars-sized body impacted our nascent planet about 4.5 billion years ago, and the resulting debris formed the Moon. The similarity between water isotopes on both bodies seems to support that theory.

Near-infrared image of the Moon's surface by NASA's Moon Mineralogy Mapper on the Indian Space Research Organization's Chandrayaan-1 mission Image credit: ISRO/NASA/JPL-Caltech/Brown Univ./USGS
Near-infrared image of the Moon’s surface by NASA’s Moon Mineralogy Mapper on the Indian Space Research Organization’s Chandrayaan-1 mission. Credit: ISRO/NASA/JPL-Caltech/Brown Univ./USGS

However, according to Dr. David A. Kring, a member of the research team that was led by Jessica Barnes from Open University, this explanation can only account for about a quarter of the water inside the moon. This, apparently, is due to the fact that most of the water would not have survived the processes involved in the formation of the Moon, and keep the same ratio of hydrogen isotopes.

Instead, Kring and his colleagues examined the possibility that water-bearing meteorites delivered water to both (hence the similar isotopes) after the Moon had formed. As Dr. Kring told Universe Today via email:

“The current study utilized analyses of lunar samples that had been collected by the Apollo astronauts, because those samples provide the best measure of the water inside the Moon. We compared those analyses with analyses of meteoritic samples from asteroids and spacecraft analyses of comets.”

By comparing the ratios of hydrogen to deuterium (aka. “heavy hydrogen”) from the Apollo samples and known comets, they determined that a combination of primitive meteorites (carbonaceous chondrite-type) were responsible for the majority of water to be found in the Moon’s interior today. In addition, they concluded that these types of comets played an important role when it comes to the origins of water in the inner Solar System.

These images produced by the Lyman Alpha Mapping Project (LAMP) aboard NASA's Lunar Reconnaissance Orbiter reveal features at the Moon's northern and southern poles in the regions that lie in perpetual darkness. They show regions that are consistent with having large surface porosities — indicating "fluffy" soils — while the reddening is consistent with the presence of water frost on the surface. Credit: Southwest Research Institute
Images produced by the Lyman Alpha Mapping Project (LAMP) aboard NASA’s Lunar Reconnaissance Orbiter reveal features at the Moon’s northern and southern poles, as well as the presence of water frost. Credit: NASA/SwRI

For some time, scientists have argued that the abundance of water on Earth may be due in part to impacts from comets, trans-Neptunian objects or water-rich meteoroids. Here too, this was based on the fact that the ratio of the hydrogen isotopes (deuterium and protium) in asteroids like 67P/Churyumov-Gerasimenko revealed a similar percentage of impurities to carbon-rich chondrites that were found in the Earth’s coeans.

But how much of Earth’s water was delivered, how much was produced indigenously, and whether or not the Moon was formed with its water already there, have remained the subject of much scholarly debate. Thank to this latest study, we may now have a better idea of how and when meteorites delivered water to both bodies, thus giving us a better understanding of the origins of water in the inner Solar System.

“Some meteoritic samples of asteroids contain up to 20% water,” said Kring. “That reservoir of material – that is asteroids – are closer to the Earth-Moon system and, logically, have always been a good candidate source for the water in the Earth-Moon system. The current study shows that to be true. That water was apparently delivered 4.5 to 4.3 billion years ago.“

The existence of water on the Moon has always been a source of excitement, particularly to those who hope to see a lunar base established there someday. By knowing the source of that water, we can also come to know more about the history of the Solar System and how it came to be. It will also come in handy when it comes time to search for other sources of water, which will always be a factor when trying to establishing outposts and even colonies throughout the Solar System.

Further Reading: Nature Communications

Posted on by Fraser Cain

Weekly Space Hangout – May 27, 2016: Dr. Seth Shostak

Host: Fraser Cain (@fcain)

Special Guest:
Dr. Seth Shostak is the Senior Astronomer at the SETI Institute. He also heads up the International Academy of Astronautics’ SETI Permanent Committee. In addition, Seth is keen on outreach activities: interesting the public – and especially young people – in science in general, and astrobiology in particular. He’s co-authored a college textbook on astrobiology, and has written three trade books on SETI. In addition, he’s published more than 400 popular articles on science — including regular contributions to both the Huffington Post and Discover Magazine blogs — gives many dozens of talks annually, and is the host of the SETI Institute’s weekly science radio show, “Big Picture Science.”

Guests:
Paul M. Sutter (pmsutter.com / @PaulMattSutter)
Kimberly Cartier (@AstroKimCartier )
Jolene Creighton (fromquarkstoquasars.com / @futurism)
Nicole Gugliucci (cosmoquest.org / @noisyastronomer)
Brian Koberlein (@briankoberlein / briankoberlein.com)

Their stories this week:
“Fresh” Lunar Craters

Faintest early-universe galaxy detected

Update on NASA’s Juno Mission

Europa’s ocean may have Earth-like chemical balance

Do Primordial Black Holes Solve Dark Matter?

India Successfully Launches Tiny Reusable Space Shuttle

30 KM Wide Asteroid Impacted Australia 3.4 Billion Years Ago

MeerKAT First Images

We’ve had an abundance of news stories for the past few months, and not enough time to get to them all. So we’ve started a new system. Instead of adding all of the stories to the spreadsheet each week, we are now using a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Google+, Universe Today, or the Universe Today YouTube page.

You can also join in the discussion between episodes over at our Weekly Space Hangout Crew group in G+!