3200 Phaethon, a celestial object between asteroid and comet
– News of October 30, 2018 –
Asteroids and comets are different celestial objects. Asteroids are mostly composed of rock and metal, while comets are created from ice and dust. The orbits of comets are generally much more eccentric than those of asteroids. They are created very far from the sun, where the temperatures are low enough to allow the appearance of ice. This allows comets to create pretty tails as they approach to the sun, because of the ice evaporation. But some celestial objects seem to be between asteroids and comets. This is the case of 3200 Phaethon, an asteroid about 5 km in diameter that was discovered in 1983.
Its orbit is very eccentric for an asteroid, it looks like a comet orbit. The highest point of its orbit is well beyond Mars, while at the lowest point in its orbit, 3200 Phaethon goes much closer to the sun than Mercury. This proximity to the sun can increase the asteroid’s surface temperatures to 800°C. The asteroid is cooked by the sun, which generates a strange bluish color on its surface. It has recently been noted that 3200 Phaethon has a small tail of dust when it goes near the sun. That’s why this asteroid has sometimes been called a rocky comet.
In December 2017, 3200 Phaethon went fairly close to Earth, about 27 times the Earth-Moon distance. The observations of the asteroid have shown that 3200 Phaethon is even more unusual than previously thought. Despite its blue color, it is very dark, barely light than coal. We now believe that 3200 Phaethon is the source of the Geminid meteor shower observed every year in December. But meteor showers are usually attributed to comets. It was therefore assumed that Phaethon was the dead nucleus of a extinct comet for a very long time. Comets and their nucleus have a color approaching red, while Phaethon is one of the blueest asteroids that has been observed.
Phaeton’s orbit and meteor shower reminds us of comets, while its color and composition are reminiscent of an asteroid. We must elucidate this mystery. How can an asteroid be the parent of a meteor shower ? What is the story of such a singular object ? It is the Japanese space agency that will try to answer these questions with the mission DESTINY+, a demonstrator of technologies that will be interested in interplanetary dust. This spacecraft should be launched in 2022. During its mission, it will approach only 500 km from Phaethon. This close passage will be an opportunity to discover what mechanisms are at the origin of its tail of dust. We hope that it will be enough to know the origin and the status of this very singular celestial object.
Astronomers discover moons around an asteroid
– News of September 12, 2017 –
The asteroid (3122) Florence crossed the earth’s orbit, passing only 7 million kilometers from us. It is the largest asteroid to go near Earth since NASA launched its Near-Earth asteroid research program in 1995. The asteroid would have done a lot of damage if it had impacted the Earth. To the surprise of the astronomers who could observe it closely during its passage in the Earth neighborhood, the asteroid has two moons which measure 100 and 300 meters. These moons were probably formed after an impact on the asteroid itself. (3122) Florence is of fairly round shape with a large crater and a ridge line. It goes near the Earth from outside its orbit.
Asteroids and comets represent a danger difficult to estimate for our planet. Relatively small objects enter the atmosphere very regularly, and those that are not completely disintegrated can cause significant damage. The meteor of Tcheliabinsk, a 15-meter-long meteor, exploded in 2013 over the Urals, causing extensive damage. The released energy has been estimated at about 30 times Hiroshima. The shock wave broke a large number of windows, causing more than a thousand wounded. This asteroid is nevertheless relatively small and of low mass. It is suspected that a similar event devastated Siberia on June 30, 1908. The explosion, much more powerful than in 2013, had cut down nearly 60 million trees on nearly 100 km of forest. It is estimated that a meteorite of 60 to 190 meters in diameter is responsible for the event which corresponded to an explosion releasing as much energy as a thousand times the bomb of Hiroshima.
If (3122) Florence collid with Earth, the damage would be immense. It is enough to see the dome-shaped surface of some bodies of the solar system to understand the incredible violence of these impacts. That is why NASA tries to inventory and monitor a large number of asteroids and comets that could be a danger to the Earth. When one of them will come, we hope that humanity will have developed a defense technology. The DART probe must impact an asteroid in 2022 in order to deflect its trajectory. This should serve as a technological demonstrator in case the situation really arises.
Image by NASA / JPL [Public Domain], via Wikimedia CommonsSources