Planetary confusion: why astronomers keep changing what it means to be a planet

Christopher Palma, Pennsylvania State University As an astronomer, the question I hear the most is why isn’t Pluto a planet anymore? More than 10 years ago, astronomers famously voted to change Pluto’s classification. But the question still comes up.

Solar System through the eyes of Hubble Space Telescope

Hubble Space Telescope was launched on April 24, 1990, and entered service on May 20, 1990. Since then, it has observed all the planets in our Solar System, apart from Earth and Mercury. Earth is far better studied by geologists on the ground and specialized probes in orbit. Hubble can’t observe Mercury as it is […]

What if Ganymede was the Earth’s second moon?

Jupiter’s moon Ganymede is the largest and most massive of the Solar System’s moons. It has a mean radius of 2634.1±0.3 km (about 1636 miles, 0.413 Earths). For comparison, our Moon’s radius is 1,737.1 km (1079 mi). What if Ganymede was the Earth’s second moon? How would it look in the sky, if it was […]

8 Things that make Life on Earth Possible

Earth, our blue planet is a tiny oasis in the vast, cold, and dark space. It is the only planet we know of that can support life. The fossil record tells us that life on Earth has lasted at least 3.5 billion years (the Earth is about 4.54 billion years old), with the oldest physical […]

Top 10 Largest Non-Planets In Our Solar System

There are eight planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Two of the largest moons are bigger than the smallest planet, Mercury. Here are the top 10 largest non-planets in our solar system (eight of them are moons and two of them are dwarf planets).