Question 2 of 21

Some scientists began hypothesizing about an unseen "Planet X" because they couldn't explain the __________.

... Scientists found some glitches in the orbits of Uranus and Neptune that could have been caused by the existence of another planet. Eventually, most scientists agreed that the irregularities were due to a miscalculation of Neptune's mass.

Question 3 of 21

One theory suggests there were originally five giant planets in our solar system instead of the originally theorized four. Under this theory, the fifth planet may have __________.

... The theory proposes that the unnamed fifth planet found itself too close to Jupiter and was pulled out of its own orbit enough to send it off into space.

Question 4 of 21

One argument that counters the existence of a "Planet X" is that _________.

... All three assertions counter the existence of Planet X. Many less-than-scientific Internet sites claim Planet X will crash into (or at least come very near to) Earth during the 2012 winter solstice. But Planet X has not been found using telescopes. Furthermore, if it were on an imminent collision course with Earth, it would be visible to the naked eye. Finally, the celestial alignment that will occur in 2012 is actually an annual event that has never had negative consequences.

Question 5 of 21

Phaeton is a hypothetical planet once thought to be located between Mars and Jupiter, a location that contains __________.

... Some scientists theorized that an asteroid belt between Mars and Jupiter contained the remains of a planet. Phaeton's existence was originally supported by the Titus-Bode law, but this law was abandoned over a century ago.

Question 6 of 21

The "Giant Impact Theory" was suggested in an attempt to explain the formation of ____________.

... Also known as the "Big Splat," this idea proposed that a smaller planet hit Earth, sending off debris, some of which became our moon.

Question 7 of 21

Planet X is also referred to as _________.

... an alternate name for Planet X, "Nibiru" purportedly comes from ancient Sumerian texts.

Question 8 of 21

The name Planet X has been used by astronomers in the past when searching for the presence of suspected planets such as ________.

... Percival Lowell, discoverer of the Mars "canals," searched for Planet X beyond Neptune for years. Pluto was located by Clyde Tombaugh years after Lowell's death.

Question 9 of 21

In 1861, astronomer Hermann Goldschmidt believed he had found the ninth moon of Saturn. Though its existence has never been confirmed, it was also reportedly seen by __________.

... No other astronomer has claimed to see Goldschmidt's moon, supposedly situated between the moons Titan and Hyperion.

Question 10 of 21

Coreless planets have been hypothesized. If they exist, they will not have ________.

... A coreless planet (consisting of just a mantle) would have no magnetic field, because the fields are formed by molten iron within a planet's core.

Question 11 of 21

The existence of planets based on carbon instead of oxygen has been conjectured. Instead of water, oceans would be made from _______.

... It has been suggested that, on a carbon planet, the oceans would consist of tar and that ice would be made of methane or carbon dioxide.

Question 12 of 21

In the 1951 film, The Man from Planet X, an Earth scientist studies the approach of another world from an observatory in ___________.

... The professor studies celestial movement from a Scottish island, where he also meets a visitor from Planet X.

Question 13 of 21

The hypothetical star Nemesis, purported to be orbiting our sun at a vast distance, is thought by some to be responsible for ____________.

... It has been posited that mass extinctions occurring every 26 million years may be due to Nemesis's orbit disrupting comets, causing them to impact earth.

Question 14 of 21

If the star Nemesis does exist, it is probably a _________.

... Theorists who support the existence of Nemesis disagree as to the type of star it is.

Question 15 of 21

Astronomers searching for Nemesis can use a _________.

... It is believed that Nemesis should be visible using only a small telescope. As it is, there are thousands of stars to evaluate to see if any even fit the criteria to be this hypothetical star.

Question 16 of 21

Theia, the possible cause of the "Big Splat," was named after a Greek titan, mother of the goddess of __________.

... In Greek mythology, Theia was mother of Selene, goddess of the moon. It has been proposed that the "Big Splat" (a smaller planet crashing into Earth) was responsible for the formation of the moon.

Question 17 of 21

Speculation about a second earth moon was adopted by author _______ for one of his novels.

... Characters in Verne's "From the Earth to the Moon" (1865) discuss Earth's second satellite.

Question 18 of 21

For more than two centuries, there was controversy over a supposed moon of Venus. It was named Neith, an Egyptian goddess of __________.

... Neith, the ancient goddess of a cult in the town of Sais, was a deity of hunting and war.

Question 19 of 21

The search for the planet Vulcan was rendered unnecessary by the ___________.

... In 1916, Einstein's general theory of relativity accounted for anomalies in the perturbation (movement) of Mercury. The unexplained movement had previously caused some to theorize that another planet, dubbed Vulcan, was causing it.

Question 20 of 21

In 1974, it was briefly suggested that Mercury had a moon. Possible evidence for it included ___________.

... Extreme ultraviolet rays were counted as evidence for a moon orbiting Mercury. Although the emissions have not been fully explained, it was nonetheless determined that the unexpected UV rays did not come from a moon.

Question 21 of 21

William Hershel, the discoverer of Uranus, also thought that he had found six moons orbiting the planet. In reality, four of the "moons" he found were ________.

... In 1787, Hershel found the largest two of Uranus' twenty-seven moons: Titania and Oberon. He mistook stars for other moons.

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