Justice: friend or foe?

The popular belief that Jupiter acts as a kind of celestial shield in the solar system, diverting asteroids and comets from the inner solar system, was examined for the first time in a series of studies that assess the degree of risk to Earth from celestial objects

The popular belief that Jupiter acts as a kind of celestial shield in the solar system, deflecting asteroids and comets from the inner solar system, was examined for the first time in a series of studies that assess the degree of risk to Earth from celestial objects.

At the European Congress of Planetary Sciences, which took place last week in Potsdam - Germany, Dr. Jonathan Horner from the Open University in Great Britain presented a study on the danger of damage to the earth-dwelling Maccentaur - an object in concentrations of asteroids and comets near Jupiter. The results indicate that the presence of Jupiter does not necessarily reduce the estimated rate of damage to the Earth.

"The idea that a Jupiter-like star plays an important role in reducing the vulnerability of stars is a widespread belief," said Dr. Horner, "but in the past, only one serious study was done on this topic, which focused on the danger from *long cycle* comets. We are conducting a long series of studies of the collision risks in star systems, first by examining our own solar system, since we know the most about it!”

The team at the European Congress has developed a computer component capable of locating a hundred thousand centaurs in the solar system. The simulation was performed five times: first with Jupiter at its current mass, once without Jupiter, then with planets that are only three-quarters the mass of Jupiter, (for comparison, the mass of Saturn is one-third the mass of Jupiter). The team found that the collision rate of bodies with a planet like Jupiter is comparable to a situation where Jupiter does not exist, that is, Jupiter has no significant effect, nevertheless when the mass of Jupiter was lower (for example, as the mass of Saturn), the Earth suffered an increase in vulnerability from the centaur belt.

"We found that if a planet with the mass of Saturn or greater were to take the place of Jupiter, the number of injuries in the country would increase." Horner said, "However, the calculations showed that even if Tzedek did not exist, there would be no change in the current rate of injury in the country. This is instead of the logical expectation that Jupiter acts as a heavenly shield. It will therefore be seen that justice gives with one hand and takes with the other."

The research shows that in a situation where there is no Jupiter-like planet, then the centaur belt will not be directed towards a cross-Earth orbit, which means that the rate of collision with the Earth will be low. Conversely, a Saturn-mass planet would provide the appropriate gravitation to inject objects into inter-Earth orbit but would not be large enough to eject these objects outside the solar system. That is, at any given time there will be more objects in orbit that cross the Earth's orbit, and therefore there will be more impacts.

However, a Jupiter-mass planet has the gravitational force to push objects out of the solar system, so if Jupiter sends objects into inter-Earth orbit, it can later eject them from the solar system and into Earth orbit.