NASA Space Observation Quiz: Near Earth Objects!

Explanation
The message suggesting that there was a chance 1997 XF11 could hit Earth in 2028 was received in 1998.

Explanation
The correct answer is 2. The risk of future impact is assessed on two scales based on orbit calculations of identified Near-Earth Objects (NEOs). These scales are the Torino Scale and the Palermo Technical Impact Hazard Scale. The Torino Scale is used to categorize the potential impact threat of NEOs on a scale from 0 to 10, while the Palermo Scale calculates the probability of a NEO impact based on its size and orbit.

Explanation
Spaceguard has been in existence since 1998.

Explanation
The initial US Congress mandate to NASA was to catalogue at least 90% of NEOs (Near-Earth Objects) that are at least 1 kilometer in size. This means that NASA was required to identify and track a significant majority of these potentially hazardous objects in order to better understand and mitigate the risk they pose to Earth.

Explanation
The question is asking about the number of planets that used to exist. According to the traditional classification, there used to be nine planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. However, in 2006, the International Astronomical Union redefined the definition of a planet, and Pluto was reclassified as a "dwarf planet." Therefore, the correct answer is 9.

Explanation
Pluto was decided by scientists to not be big enough. This is because in 2006, the International Astronomical Union (IAU) redefined the definition of a planet, and Pluto did not meet the new criteria. According to the new definition, a planet must orbit the Sun, be spherical in shape, and have cleared its orbit of other debris. Pluto failed to meet the third criterion as it shares its orbit with other objects in the Kuiper Belt. Therefore, scientists concluded that Pluto is not big enough to be considered a planet.

Explanation
There are currently three known dwarf planets in our solar system. These dwarf planets are Pluto, Eris, and Haumea. They are similar to planets in that they orbit the Sun, but they are smaller in size and have not cleared their orbits of other debris. The classification of dwarf planets was introduced by the International Astronomical Union (IAU) in 2006.

Explanation
Halley's comet appears every 76 years. This is a well-known astronomical phenomenon that has been observed for centuries. The comet was first recorded by Edmund Halley in 1705, who predicted its return based on historical observations. Since then, it has been observed multiple times, with the most recent appearance in 1986. The next predicted appearance of Halley's comet is in 2061, which will be approximately 76 years after its previous appearance.

Explanation
Asteroids travel between the orbits of Mars and Jupiter. This region is known as the asteroid belt, which is located between the innermost and outermost planets of our solar system. The gravitational pull from Jupiter prevents the asteroids from forming into a planet, causing them to remain scattered throughout this region.

Explanation
Ceres, the largest object in the asteroid belt between Mars and Jupiter, has a diameter of 950km. This measurement indicates the distance across the widest point of the celestial body.