Our atmosphere is very different from that of planets such as Venus and Mars. What makes our atmosphere so special?
Rock of Ages
A natural fission reactor allows us to look at physical constants over time, and through it we can put astrophysics to the test.
Deep Impact
There’s new evidence that a large meteor impact occurred in Australia about 350 million years ago, but the findings are not without controversy.
Somewhere Across the Sea
When we look at the Moon, we see a surface pocked with craters, scattered between seas of basalt from ancient lava flows. Since the Moon is not geologically active, it’s easy to imagine that the formation of lunar seas was triggered by large impacts. That’s actually been the dominant theory for some time. Now new research indicates that for at least one of the great seas, Oceanus Procellarum, that isn’t the case.
Rare Earth
About 1.85 billion years ago, in what would come to be known as Sudbury Canada, a 10 kilometer wide asteroid struck with such energy that it created an impact crater 250 kilometers wide. Today the chief industry of Sudbury is mining, all because of that ancient impact. In fact much of the mining industry is possible because of asteroid impacts in Earth’s early history.
Ups and Downs
The Sun orbits the center of the Milky way at a speed of about 230 km/s, taking about 250 million years to go around the galaxy once. It is a period of times sometimes referred to as a galactic year. But the Sun does not move in a simple circle or ellipse as the planets move around the Sun. This is due to the fact that the mass of the galaxy is not concentrated at a single point, but is instead spread across a plane with spiral arms and such. As a result, while the Sun orbits the galaxy it also moves up and down across the galactic plane. While the Sun is above the plane, the mass of the galaxy works to move it downward, and when below the plane the mass pulls it upward. As a result the Sun oscillates through the galaxy, crossing the galactic plane once every 30 million years or so.
Blood Ore
Hematite is a fairly common iron oxide mineral. The particular sample seen above comes from the iron range of northern Minnesota. It is about 2.7 billion years old, and is a type of hematite known as gray hematite. It doesn’t look very gray in the picture, since it has been exposed to air and water since its formation. Typically when you see hematite, it is carved and polished so that it looks like gray metallic stone, but in its raw form its surface is usually reddish in color, which is why it is also known as “blood ore.
A Rusted Development
Of the tens of thousands of meteorites that have been discovered on Earth, about a hundred came from Mars, such as the one pictured here. We know they originated from Mars because their composition is different from other meteorites, and they correlate with the atmospheric and geological composition of Mars as determined by the Martian landers. They are currently the only martian material to which we have direct access.