Planets Very Close To The Central Star

In a site known as Corral Bluffs south of Denver, Colorado, a team of paleontologists unearthed a bonanza of mammal fossils across the layer that marks the extinction event. The recovered mammal skulls indicate they were ancestors of the modern ungulates, or hoofed animals. While this analysis is approximate because there could have been larger animals that were not preserved, or are yet to be discovered, it provides an estimate of the maximum size of mammals that survived and thrived during 1 million years after the mass extinction event. A comparable increase in body size was not to occur in mammals for another 30 million years. A possible interpretation of these findings is that mammals benefited from the demise of large predators and the increasingly diverse vegetal food supply. While scientists are still a long way from achieving a full understanding of the consequences of the Chicxulub collision, these recent findings show how much still lies hidden in the terrestrial geological record. And we need not confine ourselves to the rock record on Earth to understand its formation and early development. Precious information may be retained by our neighboring planets, Mars and Venus, as we explore them further. The evolution of mammal mass around the time of the K–Pg extinction. The vertical gray line indicates the mammal maximum body mass, derived from cranial and lower first molar dimensions. Note the significant increase in size within 700,000 years following the mass extinction. Skulls from Corral Bluffs, Colorado, belonging to different mammals that roamed between 300,000 and 700,000 years after the Chicxulub event.

After The Thunder

The drawings are artist’s impressions of how these mammals might have looked. These quests may reveal more clearly fundamental processes that could have operated on the early Earth. Alongside these goals they will also search for local resources that could help sustain a future human colony. Venus, Earth’s sister planet, has received less attention. The ultimate reason for this is its unforgiving conditions, with scorching hot temperatures and a corrosive atmosphere. Venus is unlikely to host life today, but it is entirely possible that it could have had water and perhaps even life in a distant past. Is Venus the result of a more powerful Chicxulub event? Alas, we will only be able to answer this question by studying rocks from Venus’s surface. Until then, we can only speculate. We know that Venus is a bit smaller than the Earth and does not have a moon. As we noted earlier, this may suggest that Venus did not experience a last giant impact, as the Earth did, cutting short its growth. This could have far more important consequences than mass balance. Such events can stir large amounts of volatiles, including water, with important consequences for the formation of oceans.

Don't Stop Believing

Or perhaps Venus was hit by a few more and larger planetesimals during its first billion years of evolution. Scientists hope that future missions to Venus may be able to perform these measurements. We need to ask, what is the most common type of rocky planet in the Galaxy? Out there, circling other stars, are planets far more bizarre than we are accustomed to in our Solar System. These exoplanets are very far from the Earth, but many have been found. We have yet to see an image of an exoplanet. For example, the minuscule wobble of a star could indicate the presence of a nearby planet. Or a star’s slightest dimming may reveal a planet passing in front. Astronomers have monitored only a tiny number of stars, but they have found that exoplanets are very common. Among the 4,300 confirmed exoplanets known to date, most are more massive than Jupiter and thus likely to be gaseous. When a planet transits in front of the central star, its dimming is proportional to the area, and hence the radius, of the planet. And the planet’s mass is constrained by measuring the wobble of the star. Obviously, the smaller and less massive the planet, the harder it is to perform these combined observations.

If Its Good Enough For You

To put things in perspective, the Earth transiting the Sun blocks off about 0.008 percent of the solar flux, while Jupiter blocks about 1 percent of the flux. Kepler achieved an unprecedented precision of 0.003 percent. Kepler 10 b has a radius of 1.4 times that of the Earth, and is 4.6 times more massive. The planet zips around the star every 20 hours, implying a distance of about 1/20th that of Mercury from the Sun. The surface of the planet is a scorching 2,000° C, enough to melt rocks and iron. Kepler 10 hosts at least one other planet. Kepler 36 b is 50 percent larger than Earth, with a density of 7.46 g/cm3, similar to iron, and an orbital period of 13.8 days. Kepler 36 c is about twice as massive but with a density of 0.9 g/cm3 and an orbital period of 16.2 days. Perhaps the innermost, smallest planet has lost a gaseous envelope, leaving behind a predominantly naked, rocky, and metallic core. These planets, whose densities are currently unknown, are crammed in close to the star, and the outermost has an orbital period of just 1.8 days. This is not too far from the conditions in which certain terrestrial ‘extremophile’ microbes can thrive, and it is conceivable that similar organisms could live in cooler niches on the Kepler 42 planets. Kepler 20 is a star slightly cooler than the Sun in Lyra, hosting six planets. Among them, Kepler 20 e is the first planet smaller than the Earth ever detected, with a radius of 0.87 that of the Earth. Another star in Lyra, Kepler 62, hosts five planets at the time of writing. The other planets range in size from half to twice the size of the Earth. K2 229 hosts three planets in Virgo. The innermost, K2 229 b, is 30 percent larger than the Earth and 2.6 times more massive, implying that the body’s iron core makes up about 70 percent of its total mass, very much like Mercury. The gray circles indicate a selection of exoplanets with known radius, and potentially clement surface temperatures. Exoplanets are sorted vertically by increasing distance from Earth, from about 41 to 2900 light years.