Technology Review | The Physics arXiv Blog | kfc | 2011 Aug 22
Life-carrying rocks ejected from Earth by asteroid impacts could have made their way to Jupiter and beyond
Astronomers have long studied meteorites that have clearly come from the Moon and Mars. These are the result of massive asteroid impacts which eject material with such force that it ends up in interplanetary space, eventually being washed up here.
This raises an interesting question: how much Earth ejecta could have ended up elsewhere in the Solar System?
Various astronomers have studied this question by simulating how far test particles can travel after being ejected from Earth. Their conclusion is that it's relatively easy for bits of Earth to end up on the Moon or Venus. But very little would get to Mars because it would have to overcome both the Sun and the Earth's gravity.
Today, Mauricio Reyes-Ruiz at the Universidad Nacional Autonoma de Mexico and a few pals reveal the results of the biggest simulation of Earth ejecta ever undertaken. And they have a surprise.
These guys have created a computer model in which 10,242 test particles are ejected from Earth into the Solar System. They've run the model five times, increasing the average velocity of the ejected particles each time.
What they've found is quite a surprise. First up, the number of particle that end up on Mars is two orders of magnitude greater than previous studies have found.
But the biggie is that, at higher ejection speeds, particles are much more likely to end up hitting Jupiter than Mars.
That could have significant implications for the possibility that life on Earth could have travelled elsewhere. In these simulations, the Mexican team followed the test particles for up to 30,000 years, which is the length of time that astrobiologists believe Earth's hardiest lifeforms might survive in space.
So that raises the possibility that Earth could have seeded life on Jovian moons such as Europa, which many astronomers believe has a large ocean. However, the Mexican team doesn't simulate the number of particles that hit Jovian moons, only Jupiter itself.
Another surprise is that, at the higher ejection speeds, many particles end up leaving the Solar System entirely. In fact, far more end up in interstellar space than on all the planets combined, including those that return to Earth.
If these particles can preserve life from Earth for even longer periods than astrobiologists think, then at this very moment, life from Earth could be speeding its way towards distant stars.
Simulation shows how Earth may have seeded life on other planets
PhysOrg | Lisa Zyga | 2011 Aug 23
When comets and asteroids impact Earth, we’re usually most concerned with how the impact events have affected life here. But scientists have pointed out that these impact events can eject pieces of Earth’s crust containing biological organisms into space, and if ejected at the right velocities from the right location on Earth, the ejected material could collide with another planet and seed life elsewhere in the Solar System. By using new simulations to analyze the dynamics of these ejected particles, and by tripling the number of particles compared with previous studies to improve the statistics, researchers have found that particles could not only reach Venus, the Moon, and Mars, but for the first time they show that particles from Earth could also reach Jupiter.
Mauricio Reyes-Ruiz at the Universidad Nacional Autonoma de Mexico and coauthors have posted their study on the collision probabilities of particles ejected from Earth with other nearby planets at arXiv.org.
In addition to showing that particles ejected from Earth could reach Jupiter, their simulations also showed that the number of particles ejected from Earth that collide with Mars is two orders of magnitude greater than previous studies have found. The researchers explain that both results have astrobiological significance, especially due to the evidence for life-sustaining environments on early Mars and on Jupiter’s moons Europa and Ganymede.
In their simulations, the researchers analyzed 10,242 particles with a minimum ejection velocity of 11.2 km/s (which is required to escape Earth’s orbit). Different impact events throughout Earth’s history have ejected particles with a wide range of velocities, with the maximum determined by the speed of the impactor as it hits Earth. The researchers followed the simulated ejected particles for 30,000 years, which is the maximum estimated survival time for biological material in space.
Calculations have shown that an ejection velocity of 11.62 km/s is needed to reach Mars and 14.28 km/s to reach the orbit of Jupiter. While particles with ejection velocities of around 11.2 km/s have the highest chance of falling back to Earth, particles with ejection velocities of greater than 16.4 km/s typically get launched entirely out of the Solar System. Since these particles spend a very short amount of time in the inner Solar System, their collision probability with other planets is negligible.
The results of the simulation also showed that the probability of particles ejected from Earth colliding with other planets depends on the particular place on Earth from where the particles are ejected. Particles ejected from Earth’s leading face along its direction of motion, which are statistically more likely, have a higher probability of colliding with Mars and Jupiter, while particles ejected from the trailing face are more likely to impact Venus.
The researchers note that, overall, the probability of particles ejected from Earth colliding with another planet is very small. Further studies will be needed to investigate the velocity distribution of the ejected particles, along with simulations that use a greater number of ejected particles to estimate collision rates that have greater statistical significance.
Dynamics of escaping Earth ejecta and their collision probability with different Solar System bodies - M. Reyes-Ruiz et al
- arXiv.org > astro-ph > arXiv:1108.3375 > 17 Aug 2011
Earth Could Spread Life Across The Milky Way
Universe Today | Tammy Plotner | 2011 Sept 01