New Horizons: Will it solve these three mysteries about Pluto?

What is that 'whale' or the 'donut' spotted on Pluto? NASA mission control confirms that the Pluto flyby sequence has begun.

NASA’s New Horizons mission, the first of its kind to explore the Kuiper Belt beyond Neptune, is officially in countdown mode as the mission advances closer to Pluto, preparing for the July 14 flyby. As the mission draws closer to the icy planet, here are three enduring mysteries that scientists hope to solve.

1. What are the mysterious dark spots the size of Missouri made of?

New color photographs released from the mission at the beginning of July revealed a series of dark spots about 300 miles in diameter, something scientists had not seen before. The spots lay near the equator and resemble shapes seen by impact craters and volcanoes, but the New Horizons team is waiting for more detailed photographs to interpret the features.

2. What are “the whale,” “the donut,” and that bright white spot?

Somewhat blurry images taken from June 27 to July 3 have helped astronomers create a map of the planet in preparation for the upcoming flyby. The images now show an elongated area 1,860 miles (3,000 kilometers) in length, which the team has dubbed “the whale.” Immediately next to the whale’s “head” is the brightest region that has been seen on the planet, "the donut." The circular area is about 990 miles (1,600 kilometers) across, and could be a bright coating created from frozen methane, nitrogen and/or carbon monoxide as NASA’s New Horizons mission update suggests.

‘It’s easy to imagine you’re seeing familiar shapes in this bizarre collection of light and dark features. However, it’s too early to know what these features really are.’ said John Spencer of the Southwest Research Institute, Boulder, Colorado, deputy leader of the Geology, Geophysics and Imaging team to NASA.

3. How big is Pluto’s atmosphere?

The “outer limit” of Pluto’s atmosphere is hard to measure because it may be completely different from Earth’s atmosphere. According to Michael Summer, a New Horizon’s co-investigator, “If one defines it similar to the way we define the exobase of Earth’s atmosphere, then Pluto’s atmosphere has an outer limit of at least seven times Pluto’s radius above it surface. This means that the volume of Pluto’s atmosphere is over 350 times the volume of Pluto itself!” Currently, scientists are uncertain about the size of the atmosphere of the frigid planet, and hope to solve the mystery on this mission.

The New Horizons mission is the first of its kind to explore the icy bodies that are found mostly in the Kuiper Belt beyond Neptune. It is believed that these planets reflect what other worlds, including Earth, were like before the planets condensed. Scientists hope to sample the chemical clues locked in these frozen tundras to gain a glimpse of what Earth and other planets were like in their primitive years. Exploration of these types of planets was placed on NASA’s list of most important missions for this decade, according to the New Horizons press site.

As of Wednesday morning, the New Horizons spacecraft was less than 4.6 million miles from Pluto.