Model proposes that Mars was originally imported to the inner solar system
As if being another planet wasn’t alien enough, astronomers are proposing that Mars may have been born on the other side of the asteroid belt. The red planet, while nice and firm like Mercury, Venus and Earth, is apparently made of ingredients that just don’t seem to have been available in our neck of the solar system 4.5 billion years ago. So while we’re looking at Mars as the next best thing to Earth in the current time frame, there’s a chance it was created in significantly circumstances from our home planet.
The differences in composition aren’t terribly dramatic— Martian iron is still iron, as is nitrogen, oxygen or any other element. What’s different is the specific varieties of some of those elements. Atoms can have different numbers of neutrons in their nucleus, and as long as they have the same number of protons, will behave as the same element. Each possible variation of an atom is known as an isotope, and their abundance can help scientists trace where specific atoms came from. So when Martian meteorites turned up with different ratios of oxygen isotopes than you find on Earth, the hypothesis is that Mars was formed under different conditions than our planet. The catch was to figure out where that could be that could still place Mars in it’s current orbit.
The leading theory of our solar system’s origins include a period of time when Jupiter was loose, moving closer and farther from the Sun. If true, this activity could have cleared space for the inner planets like Earth and Venus, and is thought to have also pulled Mars to it’s current position as Jupiter moved out towards the pull of Saturn billions of years ago. Since that would mean Mars was created in the same space as Earth and Venus though, researchers have looked at less probable timelines in their simulations. While statistically unlikely, the best fit would be that Mars formed from cosmic leftovers further away from the Sun, and Jupiter’s movement pulled it in towards the Sun as things settled into their current orbits.
Lacking the warmth for life
If this long-shot is true, it could have implications for the origins of life on Earth. One hypothesis for early life on our planet is that existed first on Mars, and was then delivered via meteorite where it took hold in our primordial seas. If Mars was born further away from the Sun, it probably didn’t have enough heat and liquid water to be supporting and seeding life, at least not long enough for life to have evolved in the first place.
To settle some of these questions, we need more data from more sources in the solar system. Unfortunately, no missions are slated to retrieve analogous information about Venus’ isotopes, so that we could really confirm if Mars is the oddball this hypothesis suggests.
Source: Mars may not have been born alongside the other rocky planets by Thomas Sumner, Science News