earth

In August 1924, the US government declared a "National Radio Silence Day" to detect extraterrestrial signals. Civilians were asked to keep radio silence for five minutes on the hour, every hour, for 36 hours. The US Naval Observatory lifted a radio receiver three kilometers off the ground to detect Martian signals; they even had a cryptographer on hand to translate messages. Unfortunately, there was only silence, but as technology improves, so do our chances of finding life out there.

Scanning the airwaves for messages could put us in contact with other intelligent life, but what is the likelihood that any life is out there? New research led by astronomy PhD student Erik Petigura suggests it's more likely than previously thought. Petigura used NASA's Kepler telescope to look for Earth-like planets. Kepler, an observatory launched into space in 2009, was designed to survey the Milky Way for exoplanets. Without interference from the Earth's gravitational pull, ambient light, and the various celestial figures that can get in the way of measurements (like the Sun and the Moon), Kepler has a much better view of the cosmos than any Earth-bound telescope.

The diversity of life is one of the most striking aspects of our planet; hence knowing how many species inhabit Earth is among the most fundamental questions in science. Yet the answer to this question remains enigmatic, as efforts to sample the world's biodiversity to date have been limited and thus have precluded direct quantification of global species richness, and because indirect estimates rely on assumptions that have proven highly controversial.

Via Huffington Post:

The irregularly shaped hole spans about 400,000 kilometers (250,000 miles) at its widest point, said Dr. C. Alex Young, associate director for science for the heliophysics division at the space agency's Goddard facility in Greenbelt, Maryland. Its total surface area is about 410 times that of the Earth, he said (see below for size comparison).