Dawn Starts Steep Descent to Most Dazzling Orbit of Ceres

The most dazzling views ever seen of dwarf planet Ceres and its mysterious bright spots are what’s on tap by year’s end as NASA’s amazing Dawn spacecraft starts a gradual but steep descent over the next two months to its lowest and final orbit around the bizarre icy body.

Engineers at NASA’s Jet Propulsion Laboratory (JPL) successfully fired up the probes exotic ion propulsion system to begin lowering Dawn’s orbital altitude to less than a quarter of what it has been for the past two months of intense mapping operations.

On Oct. 23, Dawn began a seven-week-long dive that uses ion thruster #2 to reduce the spacecrafts vantage point from 915 miles (1,470 kilometers) at the High Altitude Mapping Orbit (HAMO) down to less than 235 miles (380 kilometers) above Ceres at the Low Altitude Mapping Orbit (LAMO).

Dawn is slated to arrive at LAMO by mid-December, just in time to begin delivering the long awaiting Christmas treats.

Ceres has absolutely tantalized researchers far beyond their wildest expectations.

When Dawn arrives at LAMO it will be the culmination of an eight year interplanetary voyage that began with a blastoff on September 27, 2007 by a United Launch Alliance (ULA) Delta II Heavy rocket from Space Launch Complex-17B (SLC-17B) at Cape Canaveral Air Force Station, Florida.

LAMO marks Dawn’s fourth, lowest and final science orbit at Ceres where the highest resolution observations will be gathered and images from the framing camera will achieve a resolution of 120 feet (35 meters) per pixel.

Dawn’s low altitude mapping orbit LAMO. This shows how the orbit naturally shifts slightly (relative to the sun) during the three months of LAMO, starting in blue and ending in red. The spacecraft completes each revolution in 5.5 hours, and Ceres rotates in 9.1 hours, so Dawn will be able to view the entire surface. Credit: NASA/JPL
Dawn’s low altitude mapping orbit LAMO. This shows how the orbit naturally shifts slightly (relative to the sun) during the three months of LAMO, starting in blue and ending in red. The spacecraft completes each revolution in 5.5 hours, and Ceres rotates in 9.1 hours, so Dawn will be able to view the entire surface. Credit: NASA/JPL

At LAMO, researchers hope to finally resolve the enduring mystery of the nature of the bright spots that have intrigued science and the general public since they were first glimpsed clearly early this year as Dawn was on its final approach to Ceres.

Dawn arrived in orbit this past spring on March 6, 2015.

This image was taken by NASA's Dawn spacecraft of dwarf planet Ceres on Feb. 19 from a distance of nearly 29,000 miles (46,000 km). It shows that the brightest spot on Ceres has a dimmer companion, which apparently lies in the same basin. See below for the wide view. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
This image was taken by NASA’s Dawn spacecraft of dwarf planet Ceres on Feb. 19 from a distance of nearly 29,000 miles (46,000 km). It shows that the brightest spot on Ceres has a dimmer companion, which apparently lies in the same basin. See below for the wide view. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

The science team has just released a new mosaic of the brightest spots on Ceres found at Occator crater and the surrounding terrain – see above.

The images were taken from the HAMO altitude of 915 miles (1,470 kilometers) during the first of six mapping cycles. They have a resolution of 450 feet (140 meters) per pixel.

Occator measures about 60 miles (90 kilometers) across and 2 miles (4 kilometers) deep.

This image, made using images taken by NASA's Dawn spacecraft during the mission's High Altitude Mapping Orbit (HAMO) phase, shows Occator crater on Ceres, home to a collection of intriguing bright spots.  Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
This image, made using images taken by NASA’s Dawn spacecraft during the mission’s High Altitude Mapping Orbit (HAMO) phase, shows Occator crater on Ceres, home to a collection of intriguing bright spots. Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Because the spots are so bright they are generally overexposed. Therefore the team took two sets of images, with shorter and longer exposure times, to maximize the details of the interior of Occator.

“This view uses a composite of two images of Occator: one using a short exposure that captures the detail in the bright spots, and one where the background surface is captured at normal exposure.”

The bright spots at Occator crater remain the biggest Cerean mystery.

So far the imagery and other science data may point to evaporation of salty water from the interior as the source of the bright spots.

“Occasional water leakage on to the surface could leave salt there as the water would sublime,” Prof. Chris Russell, Dawn principal investigator told Universe Today exclusively.

“The big picture that is emerging is that Ceres fills a unique niche.”

“Ceres fills a unique niche between the cold icy bodies of the outer solar system, with their rock hard icy surfaces, and the water planets Mars and Earth that can support ice and water on their surfaces,” Russell, of the University of California, Los Angeles, told me.

Dawn has peeled back Ceres secrets as the spacecraft orbits lower and lower. Detailed measurements gathered to date have yielded global mineral and topographic maps from HAMO with the best resolution ever as the science team painstakingly stitched together the probes spectral and imaging products.

And the best is yet to come at LAMO.

At HAMO, Dawn’ instruments, including the Framing Camera and Visible and Infrared Spectrometer (VIR) were aimed at slightly different angles in each mapping cycle allowing the team to generate stereo views and construct 3-D maps.

“The emphasis during HAMO is to get good stereo data on the elevations of the surface topography and to get good high resolution clear and color data with the framing camera,” Russell explained.

This view from NASA's Dawn spacecraft is a color-coded topographic map of Occator crater on Ceres. Blue is the lowest elevation, and brown is the highest. The crater, which is home to the brightest spots on Ceres, is approximately 56 miles (90 kilometers wide).  Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
This view from NASA’s Dawn spacecraft is a color-coded topographic map of Occator crater on Ceres. Blue is the lowest elevation, and brown is the highest. The crater, which is home to the brightest spots on Ceres, is approximately 56 miles (90 kilometers wide). Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Dawn is Earth’s first probe in human history to explore any dwarf planet, the first to explore Ceres up close and the first to orbit two celestial bodies.

The asteroid Vesta was Dawn’s first orbital target where it conducted extensive observations of the bizarre world for over a year in 2011 and 2012.

Ceres is a Texas-sized world, ranks as the largest object in the main asteroid belt between Mars and Jupiter, and may have a subsurface ocean of liquid water that could be hospitable to life.

This map-projected view of Ceres was created from images taken by NASA's Dawn spacecraft during its high-altitude mapping orbit, in August and September, 2015.  This color coded map can provide valuable insights into the mineral composition of the surface, as well as the relative ages of surface features.  Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
This map-projected view of Ceres was created from images taken by NASA’s Dawn spacecraft during its high-altitude mapping orbit, in August and September, 2015. This color coded map can provide valuable insights into the mineral composition of the surface, as well as the relative ages of surface features. Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

The mission is expected to last until at least March 2016, and possibly longer, depending upon fuel reserves.

“It will end some time between March and December,” Dr. Marc Rayman, Dawn’s chief engineer and mission director based at NASA’s Jet Propulsion Laboratory, Pasadena, California, told Universe Today.

Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.

Ken Kremer

Dawn at Ceres
An artist’s conception shows NASA’s Dawn spacecraft flying above Ceres. This view incorporates actual imagery from the Dawn mission. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Invest a Night in Vesta

The brightest asteroid visible from Earth prowls across Cetus the Whale this month. Vesta shines at magnitude +6.3, right at the naked eye limit for observers with pristine skies, but easily coaxed into view with any pair of binoculars. With the moon now gone from the evening sky, you can start your search tonight. 

4 Vesta - its formal designation as the fourth asteroid discovered - travels along a short arc just south of the easily-found star Iota Ceti this month. Use this map to help you find Deneb Kaitos, Cetus' brightest star, and from their to Iota Ceti and Vesta. Source: Stellarium
Facing southeast around 10 p.m. local time in early October. 4 Vesta — its formal designation as the fourth asteroid discovered — travels along a short arc south of the easily-found star, Iota Ceti. Shoot a line from the Square of Pegasus south to arrive at Deneb Kaitos, Cetus’ brightest star, and from their to Iota Ceti and Vesta. Detailed map below. Source: Stellarium

Vesta came to opposition on September 28 and remains well-placed for viewing through early winter. Today’s it’s 134 million miles (225 million km) from Earth or about 5 million miles farther the Mars’ average distance from us. Although it’s one of the largest asteroids in the inner asteroid belt between Mars and Jupiter with a diameter of 326 miles (525 km), it never appears larger than a point of light even in many professional telescopes. Your binocular view will be as satisfying as the one through Mt. Palomar.

A spectacular central peak more than 14 miles high rises from the 310-mile-wide crater Rheasilvia. Credit: NASA
Like an inverted belly button, a spectacular central peak more than 14 miles high rises from the 310-mile-wide crater Rheasilvia. Credit: NASA

Discovered by the German astronomer Heinrich Olbers in March 1807, Vesta was named for the Roman goddess of home and hearth. NASA’s Dawn spacecraft, currently in orbit around another asteroid, Ceres, visited Vesta between July 2011 and September 2012, taking thousands of close-up images and measuring the mineral make-up of its soil and crust. We learned a few things while we were there:

  • Vesta is differentiated into crust, mantle and core just like the bigger planets are. That’s why you’ll sometimes hear it described as a “protoplanet”, the first of its kind discovered in our solar system.
  • A class of igneous meteorites fallen to Earth called Howardites, eucrites and diogenites (HED-meteorites) were confirmed as actual pieces of the asteroid that found their way here after being blasted into space by impact.
  • Some of the meteorites / rocks that pelted the asteroid from elsewhere in the solar system are water-rich.
  • Vesta’s covered in craters like the moon
  • A staggering-large 310-mile-wide (500 km) impact crater named Rheasilvia marks its south pole. The basin’s central peak rises to 14.3 miles (23 km), more than twice the height of Mt. Everest.
  • Gullies found on its surface suggest ancient water flows.
Cornelia Crater on the large asteroid Vesta. The crater is about 4 to 5 million years old. On the right is an inset image showing an example of curved gullies, indicated by the short white arrows, and a fan-shaped deposit, indicated by long white arrows. The inset image is about 0.62 miles (1 kilometer) wide.
Cornelia Crater on the asteroid Vesta. The crater is about 4 to 5 million years old. On the right is an inset image showing an example of curved gullies that may have been carved by water, indicated by the short white arrows, and a fan-shaped deposit, indicated by long white arrows. The inset image is about 0.62 miles (1 km) wide. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

You can see it all in your mind’s eye the next clear night. For skywatchers at mid-northern latitudes, Vesta climbs into good view around 10 o’clock in early October and 8 o’clock by month’s end. If you’re familiar with gangly Cetus, you can start with the 2nd magnitude star Deneb Kaitos, the brightest star in the constellation. If not, begin your Vestan voyage from the Great Square in Pegasus, high in the southeastern sky.

Once you've arrived at Deneb Kaitos, locate Iota Ceti, 10 degrees to the northwest. The star makes finding Vesta easy in binoculars this month. Source: Chris Marriott's SkyMap software
Once you’ve arrived at Deneb Kaitos, locate Iota Ceti, 10 degrees to the northwest. The star makes finding Vesta easy in binoculars this month. Stars shown to magnitude +7. North is up and the asteroid’s position is marked every 5 days  at 10 p.m. Vesta fades slowly during the month to mag. 6.8 by Nov. 1. CDT. Source: Chris Marriott’s SkyMap software

Drop a line through the two stars along the left side of the Square and continue it down toward the southern horizon. You’ll run right into DK. Now elevate your gaze — or aim your binoculars — one outstretched fist (10°) or about two binocular fields of view above and right of Deneb Kaitos to find Iota Ceti (mag. 3.6).

Once you’ve got Iota, the asteroid will be in your field of view close by. Use the detailed chart to pinpoint its location with respect to Iota. Easy, right? Well, I hope so. Bon voyage to Vesta!

What is the Asteroid Belt?

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.

Discovery:

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 1780’s.

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.

Ceres (left, Dawn image) compared to Tethys (right, Cassini image) at comparative scale sizes. (Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA and NASA/JPL-Caltech/SSI. Comparison by J. Major.)
Ceres (left, Dawn image) compared to Tethys (right, Cassini image) at comparative scale sizes. Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA and NASA/JPL-Caltech/SSI. Comparison by J. Major.

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.

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

Structure:

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 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. It’s 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.

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.

Composition:

Most asteroids are composed of rock, but 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.

Vesta seen from the Earth-orbit based Hubble Space Telescope in 2007 (left) and up close with the Dawn spacecraft in 2011. Hubble Credit: NASA, ESA, and L. McFadden (University of Maryland). Dawn Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA. Photo Combination: Elizabeth Howell
Vesta seen from the Earth-orbit based Hubble Space Telescope in 2007 (left) and up close with the Dawn spacecraft in 2011. Hubble Credit: NASA, ESA, and L. McFadden (University of Maryland). Dawn Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA. Photo Combination: Elizabeth Howell

The 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, and their spectra matches the primordial composition of the early Solar System.

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 predicted appear to be 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 is believed to have involve collisions between larger objects (with a mean radius of ~10 km) that then broke up into smaller bodies.

This artist's conception shows how families of asteroids are created. Credit: NASA/JPL-Caltech
This artist’s conception shows how families of asteroids are created. Credit: NASA/JPL-Caltech

Some of the most prominent families in the asteroid belt are the Flora, Eunoma, 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 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 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, 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).

Asteroids we've seen up close show cratered surfaces similar to yet different from much of the cratering on comets. Credit: NASA
Asteroids we’ve seen up close show cratered surfaces similar to yet different from much of the cratering on comets. Credit: NASA

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 micrometres. 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.

Origin:

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.

Artist's impression of the early Solar System, where collision between particles in an accretion disc led to the formation of planetesimals and eventually planets. Credit: NASA/JPL-Caltech
Artist’s impression of the early Solar System, where collision between particles in an accretion disc led to the formation of planetesimals and eventually planets. Credit: NASA/JPL-Caltech

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, planestesimals were too strongly perturbed by Jupiter’s gravity to form a planet. These objects would therefore 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 mass equivalent to the 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).

Exploration:

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.

Artist's concept of the Dawn spacecraft arriving at Vesta. Image credit: NASA/JPL-Caltech
Artist’s concept of the Dawn spacecraft arriving at Vesta. Image credit: NASA/JPL-Caltech

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 flybys of Jupiter (which culminated in December of 1973) before becoming the first spacecraft to achieve escape velocity from the Solar System.

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 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 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 mined be 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 more objects out there to study.

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.

References:
NASA: The Asteroid Belt
NASA: Asteroid

Ceres Bright Spots Keep Their Secret Even From 2,700 miles Up

Don’t get me wrong. I love this new photo. Dawn snapped it from its second mapping orbit from 2,700 miles up on June 6. The number of craters and the detail visible in the parallel troughs snaking through the scene are breathtaking. That’s why I hate to niggle about the white spots.

While they appear larger and sharper than images taken in May from a greater distance, they’re too bright to show much new detail. I can’t help but wonder if mission scientists might adjust the exposure a bit the next time around.

Tighter crop on the 55-mile crater that's home to the cluster of white spots. Credit:
Tighter crop on the 55-mile (90-km) crater that’s home to the cluster of white spots. I applied a small amount of sharpening and toned down the spots just a little. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

When photographing bright objects here on Earth, we expose “for the highlights” or the bright areas in photos to avoid overexposure and loss of detail.

What a satisfying view! NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
What a satisfying view! This image, also taken on June 6, shows a large crater in Ceres’ southern hemisphere as well as cracks and radial fractures possibly associated with impacts. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Naturally, when you try to capture details in something bright, your background will go dark. But that might be what’s needed here – a change in exposure to reveal more detail in the spots at the expense of the landscape. Doubtless NASA will release enlarged and detailed images of these enigmatic dots later this summer. Just call me impatient.

Scientists still don’t understand the nature of the spot cluster, but reflective ice or salt remain the strongest possibilities.

What is this - the Moon? A view of craters in Ceres' northern hemisphere from June 6, 2015. Credit: Bright Spots Shine in Newest Dawn Ceres Images VIR Image of Ceres, May 2015Bright Spots in Ceres' Second Mapping OrbitCeres' Southern Hemisphere in Survey Ceres' Northern Hemisphere in Survey Craters in the northern hemisphere of dwarf planet Ceres are seen in this image taken by NASA's Dawn spacecraft on June 6, 2015. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
A lunar-like landscape in Ceres’ northern hemisphere photographed on June 6, 2015. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

“The bright spots in this configuration make Ceres unique from anything we’ve seen before in the solar system,” said Chris Russell, principal investigator for the Dawn mission. “The science team is working to understand their source. Reflection from ice is the leading candidate in my mind, but the team continues to consider alternate possibilities, such as salt.”

Images from Dawn's visible and infrared mapping spectrometer (VIR) show a portion of Ceres' cratered northern hemisphere, taken on May 16, 2015. From top to bottom, the views include a black-and-white image, a true-color view and a temperature image. The true-color view contains reddish dots that are image artifacts, which are not part of Ceres' surface.
Images from Dawn’s visible and infrared mapping spectrometer (VIR) show a portion of Ceres’ cratered northern hemisphere, taken on May 16, 2015 from 4,500 miles (7,300 km) away. From top to bottom, the views include a black-and-white image, a true-color view and a temperature image. In the bottom infrared view, the lightest areas are hottest and darkest are the coolest. Credit: NASA/JPL-Caltech/UCLA/ASI/INAF

It’s interesting to compare and contrast Ceres with Dawn’s first target asteroid, Vesta. Craters of every size dominate both small worlds, but Ceres shows evidence of a more activity in the form of relaxed crater rims (possibly due to ice deformation), landslides and collapsed structures.

Dawn takes about three days to orbit at its current 2,700 mile altitude. It will continue to take photos and make science observations until dropping into a new lower altitude of 900 miles (1, 450 km) in early August.

Dawn Does Dramatic Fly Over of Ceres, Enters Lower Mapping Orbit: Video

Video caption: This new video animation of Ceres was created from images taken by NASA’s Dawn spacecraft at altitudes of 8,400 miles (13,600 kilometers) and 3,200 miles (5,100 kilometers) away. Vertical dimension has been exaggerated by a factor of two and a star field added. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Scientists leading NASA’s Dawn mission to dwarf planet Ceres have just released a brand new animated video showing a dramatic fly over of the heavily cratered world featuring its mysterious bright spots whose exact origin and nature remain elusive.

Meanwhile, the venerable probe has just successfully entered its new and lower mapping orbit on June 3 from which researchers hope to glean hordes of new data to unravel the secrets of the bright spots and unlock the nature of Ceres origin and evolution.

Pockmarked Ceres is an alien world unlike any other in our solar system.

“Dawn completed the maneuvering to reach its second mapping orbit and stopped ion-thrusting on schedule. Since May 9, the spacecraft has reduced its orbital altitude from 8,400 miles (13,600 kilometers) to 2,700 miles (4,400 kilometers),” reported Marc Rayman, Dawn Chief Engineer/ Mission Director of NASA’s Jet Propulsion Laboratory, Pasadena, California.

“As Dawn flew 2,700 miles (4,400 kilometers) over Ceres’ north pole on June 5 that marked the beginning of the new mapping phase, and Dawn began taking photos and making other measurements on schedule.”

Each orbit of Dawn around Ceres at this second science mapping orbit lasts 3.1 days.

The new video was created by the research team based on observations of Ceres that were taken from Dawn’s initial mapping orbit, at an altitude of 8,400 miles (13,600 kilometers), as well as the most recent navigational images taken from 3,200 miles (5,100 kilometers), according to NASA.

It is based on data from over 80 images captured by Dawn’s framing cameras which were provided The German Aerospace Center (DLR) and Max Planck Institute for Solar System Research in Göttingen, Germany.

The images were used to provide a three-dimensional video view. The vertical dimension is exaggerated by a factor of two in the video.

“We used a three-dimensional terrain model that we had produced based on the images acquired so far,” said Dawn team member Ralf Jaumann of the German Aerospace Center (DLR), in Berlin.

“They will become increasingly detailed as the mission progresses — with each additional orbit bringing us closer to the surface.”

Imagery of the mysterious bright spots show them to seemingly be sheets of many spots of water ice, and not just single huge patches. The famous duo of ice spots are located inside the middle of a 57 miles (92 kilometers) wide crater situated in Ceres northern hemisphere.

Dawn is an international science mission managed by NASA’s Jet Propulsion Laboratory, Pasadena, California. The trio of science instruments are from the US, Germany and Italy.

The framing camera was provided by the Max Planck Institute for Solar System Research, Göttingen, Germany and the German Aerospace Center (DLR).

This view of Ceres was taken by Dawn spacecraft on May 23 and shows finer detail becoming visible on the dwarf planet. The spacecraft snapped the image at a distance of 3,200 miles (5,100 kilometers) with a resolution of 1,600 feet (480 meters) per pixel. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
This view of Ceres was taken by Dawn spacecraft on May 23 and shows finer detail becoming visible on the dwarf planet. The spacecraft snapped the image at a distance of 3,200 miles (5,100 kilometers) with a resolution of 1,600 feet (480 meters) per pixel. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Dawn will spend most if June at this second mapping orbit before firing up the ion engines and spiraling yet lower for a mission expected to last until at least June 2016.

Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.

Ken Kremer

Dawn’s spiral descent from its first mapping orbit (RC3) to its second (survey). The two mapping orbits are shown in green. The color of Dawn’s trajectory progresses through the spectrum from blue, when it began ion-thrusting on May 9, to red, when ion-thrusting concludes on June 3. The red dashed sections show where Dawn is coasting, mostly for telecommunications. The first two coast periods include OpNav 8 and 9. Image credit: NASA/JPL-Caltech
Dawn’s spiral descent from its first mapping orbit (RC3) to its second (survey). The two mapping orbits are shown in green. The color of Dawn’s trajectory progresses through the spectrum from blue, when it began ion-thrusting on May 9, to red, when ion-thrusting concludes on June 3. The red dashed sections show where Dawn is coasting, mostly for telecommunications. The first two coast periods include OpNav 8 and 9. Image credit: NASA/JPL-Caltech

How Dense is the Asteroid Belt?

We’ve seen way too many science fiction episodes that show asteroid belts as dense fields of tumbling boulders. How dense is the asteroid belt, and how to spacecraft survive getting through them?

For the purposes of revenue, lazy storytelling, and whatever it is Zak Snyder tells himself to get out of bed in the morning, when it comes to asteroids, Science fiction and video games creators have done something of disservice to your perception of reality.

Take a fond trip down sci-fi memory lane, and think about the time someone, possibly you, has had to dogfight or navigate through yet another frakkin’ asteroid belt. Huge space rocks tumbling dangerously in space! Action! Adventure! Only the skilled pilot, with her trusty astromecha-doplis ship can maneuver through the dense cluster of space boulders, dodging this way and that, avoiding certain collision.

And then she shoots her pew pew laser breaking up larger asteroids up into smaller ones, possibly obliterating them entirely depending on the cg budget. Inevitably, there’s bobbing and weaving. Pursuit craft will clip their wings on asteroids, spinning off into nearby tango. Some will fly straight into a space boulder.

Finally you’ll thread the needle on a pair of asteroids and the last ship of the whatever they’re called clicky clacky mantis Zorak bug people will try and catch you, but he/it won’t be quite so lucky. Poetically getting squashed like… a… bug. Sackhoff for the win, pilot victorious.

Okay, you probably knew the laser part is totally fake. I mean, everybody knows you can’t hear sounds in space. Outside of Starbuck being awesome, is that at all realistic? And if so, how does NASA maneuver unmanned spacecraft through that boulder-strewn grand canyon death trap to reach the outer planets?

The asteroid belt is a vast region between the orbits of Mars and Jupiter. Our collection of space rocks starts around 300 million kilometers from the Sun and ends around 500 million kilometers. The first asteroid, the dwarf planet Ceres which measures 950 km across, was discovered in 1801, with a “That’s funny.”. Soon after astronomers turned up many more small objects orbiting in this region at the “Oooh neat!” stage.

Artist’s concept of Dawn in its survey orbit at dwarf planet Ceres. Credit: NASA/JPL-Caltech
Artist’s concept of Dawn in its survey orbit at dwarf planet Ceres. Credit: NASA/JPL-Caltech

They realized it was a vast belt of material orbiting the Sun, with I suspect a “We’re all gonna die.”. To date, almost half a million asteroids have been discovered, most of which are in the main belt.

As mentioned in a another video, gathering up all the material in the asteroid belt and gluing it together makes a mass around 4% of the Moon. So, in case one of your friends gets excited and suggests it was a failed planet, you can bust out that stat and publicly shame them for being so 1996, Goodwill Hunting style. You like asteroids? How about them asteroids?

There’s a few hundred larger than 100 km across, and tens of millions of rocks a hundred meters across. Any one of these could ruin a good day, or bring a bad day to a welcome firey close for either a depressed wayfaring spacecraft or a little bluegreen speck of a planet. Which sounds dangerous all the way around.

Fortunately, our asteroid belt is a vast region of space. Let’s wind up the perspective-o-meter. If you divide the total number of objects in the field by the volume of space that asteroid belt takes up, each space rock is separated by hundreds of thousands of kilometers. Think of it as gravity’s remarkably spacious zen rock garden.

Ceres compared to asteroids visited to date, including Vesta, Dawn's mapping target in 2011. Image by NASA/ESA. Compiled by Paul Schenck.
Ceres compared to asteroids visited to date, including Vesta, Dawn’s mapping target in 2011. Image by NASA/ESA. Compiled by Paul Schenck.

As a result, when NASA engineers plot a spacecraft’s route through the asteroid belt, they don’t expect to make a close encounter with any asteroids – in fact, they’ll change its flight path to intercept asteroids en route. Because hey look, asteroid!

Even though Ceres was discovered in 1801, it’s never been observed up close, until now. NASA’s Dawn spacecraft already visited Asteroid Vesta, and by the time you’re watching this video, it will have captured close-up images of the surface of Ceres.

Once again, science fiction creatives sold us out to drama over hard science. If you’re passing through an asteroid belt, you won’t need to dodge and weave to avoid the space rocks. In fact, you probably wouldn’t even know you were passing through a belt at all. You’d have to go way the heck over there to even get a nearby look at one of the bloody things. So we’re safe, our speck is safe, and all the little spacecraft are safe…. for now.

Which dramatic version of “asteroids” are you most fond of? Tell us in the comments below.

Scientists in Orbit Over Dawn’s Arrival at Ceres


Dawn’s approach and trajectory as it begins its orbital “dance” with Ceres. As you watch, note the timeline at upper right.

Dawn made it! After a 14-month tour of the asteroid Vesta and 2 1/2 years en route to Ceres, the spacecraft felt the gentle tug of Ceres gravity and slipped into orbit around the dwarf planet at 6:39 a.m. (CST) Friday morning.

“We feel exhilarated,” said lead researcher Chris Russell at the University of California, Los Angeles, after Dawn radioed back the good news. 

 

Not only is this humankind’s first probe to orbit a dwarf planet, Dawn is the only spacecraft to fly missions to two different planetary bodies. Dawn’s initial orbit places it 38,000 miles (61,000 km) from Ceres with a view of the opposite side of Ceres from the Sun. That’s why we’ll be seeing photos of the dwarf planet as a crescent for the time being. If you watch the video, you’ll notice that Dawn won’t see Ceres’ fully sunlit hemisphere until early-mid April.

Dawn’s spiral descent from survey orbit to the high altitude mapping orbit. The trajectory progresses from blue to red over the course of the six weeks. The red dashed segments are where the spacecraft is not thrusting with its ion propulsion system (as explained in April). Credit: NASA/JPL - See more at: http://dawnblog.jpl.nasa.gov/2014/06/30/dawn-journal-june-30-2/#sthash.CZ2WGsDQ.dpuf
Dawn’s spiral descent from survey orbit to the high altitude mapping orbit. The trajectory progresses from blue to red over the course of the six weeks. The red dashed segments are where the spacecraft is not thrusting with its ion propulsion system. Credit: NASA/JPL

The spacecraft will spend the next month gradually spiraling down to Ceres to reach its “survey orbit” of 2,730 miles in April. From there it will train its science camera and visible and infrared mapping spectrometer  to gather pictures and data. The leisurely pace of the orbit will allow Dawn to spend more than 37 hours examining Ceres’ dayside per revolution. NASA will continue to lower the spacecraft throughout the year until it reaches its minimum altitude of 235 miles.

As Dawn maneuvers into orbit, its trajectory takes it to the opposite side of Ceres from the sun, providing these crescent views. These additional pictures were taken on March 1 at a distance of 30,000 miles (49,000 km). Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
As Dawn maneuvers into orbit, its trajectory takes it to the opposite side of Ceres from the sun, providing these crescent views. These additional pictures were taken on March 1 at a distance of 30,000 miles (49,000 km). Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

“Since its discovery in 1801, Ceres was known as a planet, then an asteroid and later a dwarf planet,” said Marc Rayman, Dawn chief engineer and mission director at JPL. “Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls Ceres, home.”

More about Dawn’s incredible accomplishment can be found in the excellent Dawn Journal, written by Dawn chief engineer and mission director Marc Rayman.

What Asteroid 2004 BL86 and Hawaii Have in Common

At first glance, you wouldn’t think Hawaii has any connection at all with asteroid 2004 BL86, the one that missed Earth by 750,000 miles (1.2 million km) just 3 days ago. One’s a tropical paradise with nightly pig roasts, beaches and shave ice; the other an uninhabitable ball of bare rock untouched by floral print swimsuits.

But Planetary Science Institute researchers Vishnu Reddy and Driss Takir would beg to differ.

Using NASA’s Infrared Telescope Facility on Mauna Kea, Hawaii they discovered that the speedy “space mountain” has a composition similar to the very island from which they made their observations – basalt.

“Our observations show that this asteroid has a spectrum similar to V-type asteroids,” said Reddy. “V-type asteroids are basalt, similar in composition to lava flows we see in Hawaii.

Minerals on the surface of an object like the moon or an asteroid absorb particular wavelengths of light to create a series of "blank spaces" or absorption lines that are unique to a particular element or compound. Credit: NASA
Minerals on the surface of an object like the moon or an asteroid absorb wavelengths of light to create a series of “blank spaces” or absorption lines that are unique to a particular element or compound. Credit: NASA

The researchers used a spectrograph to study infrared sunlight reflected from 2004 BL86 during the flyby. A spectrograph splits light into its component colors like the deli guy slicing up a nice salami. Among the colors are occasional empty spaces or what astronomers call absorption lines, where minerals such as olivine, pyroxene and plagioclase on the asteroid’s surface have removed or absorbed particular slices of sunlight.

You're looking straight down on the 310-mile-wide Rheasilvea crater / impact basin on the asteroid Vesta. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
You’re looking straight down into the 310-mile-wide (500 km) Rheasilvea crater / impact basin on the asteroid Vesta. It’s though that many of the Vesta-like asteroids, including 2004 BL86, originated from the impact. It Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

These are the same materials that not only compose earthly basalts – all that dark volcanic rock that underlies Hawaii’s reefs and resorts – but also Vesta, considered the source of V-type asteroids. It’s thought that the impact that hollowed out the vast Rheasilvia crater at Vesta’s south pole blasted chunks of mama asteroid into space to create a family of smaller siblings called vestoids.

 

This animation, created from individual radar images, clearly show the rough outline of 2004 BL86 and its newly-discovered moon. Credit: NASA/JPL-Caltech
This animation, created from individual radar images, shows the binary asteroid 2004 BL86 on January 26th.  The moon’s orbital period is about 13.8 hours. Credit: NASA/JPL-Caltech

So it would appear that 2004 BL86 could be a long-lost daughter born through impact and released into space to later be perturbed by Jupiter into an orbit that periodically brings it near Earth. Close enough to watch in wonder as it inches across the field of view of our telescopes like it did earlier this week.

The little moonlet may or may not be related to Vesta, but its presence makes 2004 BL86 a binary asteroid, where each object revolves about their common center of gravity. While the asteroid is unlikely to become future vacation destination, there will always be Hawaii to satisfy our longings for basalt.

Here’s Dawn’s Best View of Ceres Yet

Just sit back and watch the world turn… or should I say, watch the dwarf planet turn in this fascinating animation from Dawn as the spacecraft continues on its ion-powered approach to Ceres!

The images were captured by Dawn’s framing camera over the course on an hour on Jan. 13 at a distance of 238,000 miles (383,000 km) from Ceres. At 590 miles (950 km) wide Ceres is the largest object in the main asteroid belt.

“Already, the [latest] images hint at first surface structures such as craters,” said Andreas Nathues, lead investigator for the framing camera team at the Max Planck Institute for Solar System Research in Gottingen, Germany. “We have identified all of the features seen by Hubble on the side of Ceres we have observed, and there are also suggestions of remarkable structures awaiting us as we move even closer.”

Although these latest 27-pixel images from Dawn aren’t quite yet better than Hubble’s images from Jan. 2004, very soon they will be.

Comparison of HST and Dawn FC images of Ceres taken nearly 11 years apart
Comparison of HST and Dawn FC images of Ceres taken nearly 11 years apart

“The team is very excited to examine the surface of Ceres in never-before-seen detail,” said Chris Russell, principal investigator for the Dawn mission, based at the University of California, Los Angeles. “We look forward to the surprises this mysterious world may bring.”

Launched Sept. 27, 2007, Dawn previously spent over 13 months in orbit around the asteroid/protoplanet Vesta from 2011–12 and is now on final approach to Ceres. On March 6 Dawn will arrive at Ceres, becoming the first spacecraft to enter orbit around two different target worlds.

Read more: Find Out How “Crazy Engineering” is Getting Dawn to Ceres

Learn more at JPL’s Dawn mission site here, and find out where Dawn is right now here.

Also, read more from the Max Planck Institute for Solar System Research here.

Source: NASA/MPI

Surprise! Asteroid Crashes And Raindrop Splashes Look Almost Alike

It’s hard to study what an asteroid impact does real-time as you’d need to be looking at the right spot at the right time. So simulations are often the way to go. Here’s a fun idea captured on video — throwing drops of water on to granular particles, similar to what you would find on a beach. The results, the researchers say, look surprisingly similar to “crater morphology”.

A quick caution — the similarity isn’t completely perfect. Raindrops are much smaller, and hit the ground at quite a lower speed than you would see an asteroid slam into Earth’s surface. But as the authors explain in a recent abstract, there is enough for them to do high-speed photography and make extrapolations.

Although the mechanism of granular impact cratering by solid spheres is well explored, our knowledge on granular impact cratering by liquid drops is still very limited. Here, by combining high-speed photography with high-precision laser profilometry, we investigate liquid-drop impact dynamics on granular surface and monitor the morphology of resulting impact craters. Surprisingly, we find that despite the enormous energy and length difference, granular impact cratering by liquid drops follows the same energy scaling and reproduces the same crater morphology as that of asteroid impact craters.

There are of course other ways of understanding how craters are formed. A common one is to look at them in “airless” bodies such as the Moon, Vesta or Ceres — and that latter world will be under extensive study in the next year. NASA’s Dawn spacecraft is en route to the dwarf planet right now and will arrive there in 2015 to provide the first high-resolution views of its surface.

Amateurs can even collaborate with professionals in this regard by participating in Cosmoquest, an organization that hosts Moon Mappers, Planet Mappers: Mercury and Asteroid Mappers: Vesta — all examples of bodies in a vacuum with craters on them.

The research was presented at the APS Division of Fluid Dynamics annual meeting and published in the Proceedings of the National Academy of Sciences. It was led by Runchen Zhao at the University of Minnesota.