Globular clusters resemble stellar jewel boxes featuring roughly spherical assemblies of countless closely-packed stars. This example, NGC 6717, was discovered by William Herschel in 1784 and is located some 20,000 light years from Earth in the constellation Sagittarius. It is one of at least 150 globular clusters orbiting the Milky Way and a spectacular target for the Hubble Space Telescope, which captured this composite image using the Wide Field Camera 3 and the Advanced Camera for Surveys. The brighter stars with criss-cross diffraction spikes, caused by light interacting with the support vanes holding Hubble’s secondary mirror, are much closer to Earth and not part of the cluster.
Earth came early to the party in the evolving universe. According to a new theoretical study, when our solar system was born 4.6 billion years ago only eight percent of the potentially habitable planets that will ever form in the universe existed. And, the party won’t be over when the Sun burns out in another 6 billion years. The bulk of those planets — 92 percent — have yet to be born.