7. Jupiter – A powerful vacuum cleaner in solar system
Jupiter is the largest planet in the solar system. The existence of Jupiter is very important for life on Earth. The asteroid belt lies between the orbits of the Mars and Jupiter and contains numerous number of asteroids and minor planets. If they are gravitationally disturbed, they can escape from the orbit and wondering around the solar system.
If fragments of these comets or asteroids enter Earth’s atmosphere, they become meteoroids. Fig. 11 shows how often meteorites enter Earth and how much impact energy they can generate. On average, about 1 meter size meteorite enters Earth once every hour and a 10 meter size once every few years. The impact energy of the 10 meter meteorite is about 0.1 megaton of TNT or more than 10 times stronger than the Hiroshima atomic bomb. If the size of meteorite is larger than 10 meters, it will devastate a significant area on Earth.
Fig. 1.11 – Size, frequency, and impact energy of the meteorites falling to Earth.
In 1908, about 60 meter size meteoroid exploded above the ground near the Tunguska river. The explosion knocked over an estimated 80 million trees covering 2,150 square kilometers (see Fig. 1.12). The frequencies of having about 50m, 100m, 1km, and 10km meteoroid are once in a century, one thousand years, one million years, and one hundred million years, respectively. The 100m size meteoroid has an energy equivalent to a few megaton of TNT and can generate 1km impact crater and destroy about 100,000 km2 area. If it falls on the ocean, it will generate enormous tsunami.
Fig. 1.12 – Fallen trees by 60m meteorite in Tunguska event
Having Jupiter as our neighbor is important since it attracts hazardous asteroids and meteoroids that can otherwise be falling on Earth. This is because mass of the Jupiter is about 320 times massive than that of the Earth. According to calculation, Jupiter can capture comets about 5,000 time more than the Earth does. In 1994, Jupiter actually demonstrated comet (Shoemaker-Levi) capturing event. Before colliding to Jupiter, the Shoemaker-Levi comet has been fragmented and Fig. 1.13 shows fragmented Shoemaker-Levi comet observed with Hubble Space Telescope (top) and Jupiter capturing these fragments (bottom). The size of the largest fragment is about 2 km and if it has fallen to Earth, it could have destroyed the entire area of the North America.
Fig 1.13 – Comet Shoemaker-Levi (top panel), and impact sites in Jupiter (bottom panel dark spots).
Jupiter works just like a hugh vacuum cleaner in the solar system. However, if the size of the Jupiter was smaller than the current one, or its location was further away from the Earth, all or a significant fraction of life on Earth might have been extinguished long times ago.