Planets and non-Planets
There are this many planets in our Solar System.
What is eight?
This is the general name for a debris cloud orbiting a star.
What is a circumstellar disk?
These two elements are the most abundant elements in the Solar System (and universe).
What are hydrogen and helium?
The most widely accepted model of the Solar System's formation and evolution is called this.
What is the nebular hypothesis?
The outer edge of the heliosphere is known as this.
What is the heliopause?
Uranus and Neptune are collectively known by this phrase.
What are ice giants?
This circumstellar disk is located between the orbits of Mars and Jupiter.
What is the asteroid belt?
It is called a molecular cloud because it was this enough for matter to exist as molecules, mostly hydrogen gas (H2)
What is cold?
The Solar System is believed to have begun with the collapse of a giant molecular cloud, which happened approximately this long ago.
What is 4.6 billion years?
This space probe was the first human-made object to travel past the orbit of Neptune.
What is Pioneer 10?
This celestial body, located in the asteroid belt, was once classified as an asteroid, but is now considered a dwarf planet.
What is Ceres?
A circumstellar disk surrounding a new star is called this.
What is a protoplanetary disk?
Past this boundary is where volatiles can exist in condensed form.
What is the frost line?
Within 50 million years from the collapse of the molecular cloud, the protostar began doing this.
What is fusion?
This man was one of the Mercury Seven astronauts and the docking pilot of the Apollo-Soyuz Test Project.
Who is Deke Slayton?
Pluto is no longer considered a planet because it fails this criterion for planets.
What is dominating the accretion zone?
The outer edge of the Kuiper belt is located approximately this many AUs from the Sun.
What is fifty?
The rocky planets' inner layers are made of metals, and their outer layers are made of this.
What are silicates?
Uranus and Neptune likely formed closer to the orbits of Jupiter and Saturn, and then moved outward in a process known as this.
The Sun is a middle-sized star located in this arm of the Milky Way galaxy.
What is the Orion arm?
This is the oldest planet.
What is Jupiter?
This is the name of the hypothetical flat, inner edge of the Oort cloud, located about 2,000 AUs from the Sun.
What is the Hills cloud?
Only this percentage of the matter in the Solar System is made of refractory substances, which is why the rocky planets could not grow very large.
What is 0.6%?
The fragment of the giant molecular cloud that collapsed to form our Solar System was approximately this far across its length.
What is 3 light-years?
The Sun's diameter is approximately this many times larger than the Earth's.
What is 109 times?