The Lazarus Comets: Asteroid Belt a Graveyard for Comets

These illustrations show the asteroid belt in the present day and in the early Solar System, located between the Sun (at centre) and four terrestrial planets (near the Sun) and Jupiter (at bottom left). 

The top image shows the conventional model for the asteroid belt; largely composed of rocky material. 

The middle image shows the proposed model, with a small number of active comets and a dormant cometary population. 

The lower diagram shows how the asteroid belt might have looked in the early Solar System, with vigorous cometary activity. 

Credit: Ignacio Ferrin / University of Anitoquia

A team of astronomers from the University of Anitoquia, Medellin, Colombia, have discovered a graveyard of comets.

The researchers, led by Anitoquia astronomer Prof. Ignacio Ferrin, describe how some of these objects, inactive for millions of years, have returned to life leading them to name the group the 'Lazarus comets'.

The team publish their results in the Oxford University Press journal Monthly Notices of the Royal Astronomical Society.

Comets are among the smallest objects in the Solar System, typically a few km across and composed of a mixture of rock and ices.

Ignacio Ferrin

If they come close to the Sun, then some of the ices turn to gas, before being swept back by the light of the Sun and the solar wind to form a characteristic tail of gas and dust.

Most observed comets have highly elliptical orbits, meaning that they only rarely approach the Sun. Some of these so-called long period comets take thousands of years to complete each orbit around our nearest star.

There is also a population of about 500 short period comets, created when long period comets pass near Jupiter and are deflected in orbits that last anything between 3 and 200 years.

Although uncommon events, comets also collide with Earth from time to time and may have helped bring water to our planet.

The new work looked at a third and distinct region of the Solar System, the main belt of asteroids between the orbits of Mars and Jupiter.

This volume of space contains more than 1 million objects ranging in size from 1 m to 800 km.

The traditional explanation for asteroids is that they are the building blocks of a planet that never formed, as the movement of the pieces was disrupted by the strong gravitational field of Jupiter.

In the last decade 12 active comets have been discovered in the asteroid main belt region. This was something of a surprise and the Medellin team set out to investigate their origin.

Jorge Zuluaga

The team, made up of Prof. Ferrin and his colleagues Profs. Jorge Zuluaga and Pablo Cuartas, now think they have an explanation.

"We found a graveyard of comets," exclaims Professor Ferrín. He adds: "Imagine all these asteroids going around the Sun for aeons, with no hint of activity. We have found that some of these are not dead rocks after all, but are dormant comets that may yet come back to life if the energy that they receive from the Sun increases by a few per cent."

Surprisingly, this can happy fairly easily, as the orbits of many objects in the asteroid belt are nudged by the gravity of Jupiter. The shape of their orbits can then change, leading to a decrease in the minimum distance between the object and the Sun (perihelion) and a slight increase in average temperature.

Pablo Cuartas

According to this interpretation, millions of years ago the main belt was populated by thousands of active comets.

This population aged and the activity subsided. What we see today is the residual activity of that glorious past.

Twelve of those rocks are true comets that were rejuvenated after their minimum distance from the Sun was reduced a little.

The little extra energy they received from the Sun was then sufficient to revive them from the graveyard.

Prof. Ferrin describes the 12 active comets. "These objects are the 'Lazarus comets', returning to life after being dormant for thousands or even millions of years. Potentially any one of the many thousands of their quiet neighbours could do the same thing."

Journal Reference:
Ignacio Ferrin, Jorge Zuluaga, Pablo Cuartas. The location of Asteroidal Belt Comets (ABCs), in a comets' evolutionary diagram: The Lazarus Comets. Monthly Notices of the Royal Astronomical Society., 2013

Kuiper Belt Wider and More Massive than Asteroid belt

Kuiper Belt is a region in space initially predicted by astronomer Gerard P. Kuiper.

Now, this was way back in 1951. It took more than four decades before the said region was finally discovered.

In fact, it took five years of searching before David Jewitt and Jane Luu were finally successful.

Well, you can say that there are similarities between Kuiper Belt and the asteroid belt, both being composed of celestial objects.

Recent discoveries reveal that the Kuiper is much much larger than originally thought, about 20 times wider and perhaps 200 times more massive.

Also, while the asteroid belt is composed mainly of asteroids and meteoroids, which are basically made up of rock and metal, Kuiper is made up of frozen volatiles (methane, ammonia, and water). That’s right, the objects there are pretty much like comets.

Now, how did a “planet” like Pluto get to be reclassified into a KBO? First, Pluto is found right inside Kuiper. Furthermore, there are lots of objects in there that are pretty much of the same size (only slightly smaller actually) as Pluto. Finally, there are objects outside (but near) Kuiper that are larger than Pluto.

One of these objects is Eris, which is estimated to be 27% more massive than Pluto. Another object which is larger than Pluto and also believed to have been once a KBO is Triton, Neptune’s natural satellite.

We’ve mentioned earlier that most of the objects found in Kuiper have similar composition to those of comets. It would be therefore tempting to conclude that Kuiper and the Oort cloud are one. The Oort cloud is a hypothetical region believed to be the “dwelling place” of comets.

Scientists however think the Oort cloud is much much farther away. While the Kuiper Belt is in the region between 30 AU to 55 AU from the Sun, the Oort cloud is believed to be 50,000 AU from the Sun. That’s nearly one light-year away.

A deeper understanding of Kuiper should emerge once the spacecraft New Horizons reaches Pluto in July 2015. New Horizons was launched on January 19, 2006 for the purpose of exploring the Kuiper Belt.

NASA - What Is Pluto?

Pluto was discovered in 1930 by an astronomer from the United States. An astronomer is a person who studies stars and other objects in space.

Pluto was known as the smallest planet in the solar system and the ninth planet from the sun.

Today, Pluto is called a "dwarf planet." A dwarf planet orbits the sun just like other planets, but it is smaller. A dwarf planet is so small it cannot clear other objects out of its path.

On average, Pluto is more than 3.6 billion miles (5.8 billion kilometers) away from the sun. That is about 40 times as far from the sun as Earth.

Pluto orbits the sun in an oval like a racetrack. Because of its oval orbit, Pluto is sometimes closer to the sun than at other times. At its closest point to the sun Pluto is still billions of miles away.

Pluto is in a region called the Kuiper (KY-per) Belt. Thousands of small, icy objects like Pluto are in the Kuiper Belt.

Pluto is only 1,400 miles (2,300 kilometers) wide. That's about half the width of the United States. Pluto is slightly smaller than Earth's moon. It takes Pluto 248 years to go around the sun. One day on Pluto is about 6 1/2 days on Earth.

Pluto was named by an 11-year-old girl from England. The dwarf planet has three moons. Its largest moon is named Charon (KER-ən). Charon is about half the size of Pluto.

Pluto's two other moons are named Nix and Hydra. They were discovered in 2005. NASA's Hubble Space Telescope took pictures of the two new moons. Nix and Hydra are very small. The moons are less than 100 miles (160 kilometers) wide.

A drawing of the solar system shows Pluto's tilted orbit. Pluto's orbital path angles 17 degrees above the line, or plane, where the eight planets orbit. Credit: NASA

In 2003, an astronomer saw a new object beyond Pluto. The astronomer thought he had found a new planet. The object he saw was larger than Pluto. He named the object Eris (EER-is).

Finding Eris caused other astronomers to talk about what makes a planet a "planet." There is a group of astronomers that names objects in space. This group decided that Pluto was not really a planet because of its size and location in space. So Pluto and objects like it are now called dwarf planets.

Pluto is also called a plutoid. A plutoid is a dwarf planet that is farther out in space than the planet Neptune. The three known plutoids are Pluto, Eris and Makemake (MAH-kee-MAH-kee). Astronomers use telescopes to discover new objects like plutoids.

Scientists are learning more about the universe and Earth's place in it. What they learn may cause them to think about how objects like planets are grouped. Scientists group objects that are like each other to better understand them. Learning more about faraway objects in the solar system is helping astronomers learn more about what it means to be a planet.

Dawn Probe Enters the Asteroid Belt on route to date with Vesta and Ceres

After crossing the threshold of the belt earlier this month, Dawn will travel 7.7 astronomical units (AU), or nearly 1.2 billion kilometers (almost 720 million miles), to its July 2011 rendezvous with Vesta.


Yet in all that time, and across all that distance, the closest the probe will come to a catalogued asteroid is 1.0 million kilometers (greater than 600 thousand miles), or more than 2.5 times the distance between Earth and the moon.

Dawn continues to make steady progress through the solar system as it maintains a gentle pressure on its orbit around the Sun. It has spent 95% of the time since the last log thrusting with its ion propulsion system, stopping only briefly each week to communicate with the mission control team on distant Earth.

A Date with Vesta and Ceres
The probe is on an exciting journey to unlock secrets from the dawn of the solar system ensconced in the mysterious worlds Vesta and Ceres. And yet there is one aspect of this expedition that likely is much less exciting than some readers may expect.

Entered Asteroid Belt
Dawn entered the main asteroid belt on November 13. As it ventures ever deeper into this vast collection of material between Mars and Jupiter, it may be tempting to think of the spacecraft constantly dodging asteroids. In some science fiction movies, the huge rocky bodies are so close together that highly skilled piloting is required to avoid catastrophes.

Running the Gauntlet of Asteroids
Now Dawn is guided by some of the most proficient interplanetary fliers this side of Pluto, but the reality is that accidental impacts are exceedingly unlikely. Space is big, and as plentiful as asteroids are, the distances between them are tremendous.

No Close Encounters
After crossing the threshold of the belt earlier this month, Dawn will travel 7.7 astronomical units (AU), or nearly 1.2 billion kilometers (almost 720 million miles), to its July 2011 rendezvous with Vesta. Yet in all that time, and across all that distance, the closest the probe will come to a catalogued asteroid is 1.0 million kilometers (greater than 600 thousand miles), or more than 2.5 times the distance between Earth and the moon.

Certainly travellers on Earth would not consider something that far away to be a hazard (especially compared to what many Dawn team members regularly experience on the freeways in Los Angeles), and neither would our intrepid explorer.

Bound for Giants
Dawn is bound for the giants of the asteroid belt. Vesta's equatorial diameter is about 580 kilometers (360 miles), and Ceres is 975 km (605 miles) across. (Remember that when thinking about three-dimensional worlds such as these, the diameter may fail to illustrate how large they really are.)

Two Thirds of the Asteroid Mass
Together these two behemoths contain more than a third of all the mass in the main asteroid belt. On the scale of our cross-country drive, Vesta would be 2.0 meters (6.5 feet) wide and Ceres would be 3.3 meters (11 feet). Rather than missing them by great distances, we would move to within 0.6 meters (2 feet) of the first target and 2.4 meters (8 feet) of the second.

Dawn's science instruments are optimised for studying these immense bodies in detail from orbit around them, just as many Earth-observation spacecraft peer down constantly on our planet.

Diverting the probe to zip past a chunk of rock for a very brief view would be possible, but doing so would take precious time away from the far richer and more valuable investigations planned for Vesta. That is where Dawn will find the rewards of the next 20 months of travel. Stay tuned to this channel......