Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: Pluto is almost ready for its close up. After nine and a half years and three billion miles, the New Horizons spacecraft is about to lift the veil on the icy world. It promises to be the biggest planetary debut in a quarter-century. The curtain hasn't been pulled back like this since the Voyager 2 flew past Neptune in 1989. For principal investigator, Alan Stern, this is the culmination of 15 years of hard work and endless campaigns to launch missions to the dwarf planet. 'The adrenaline is intense at the moment,' Stern told DailyMail.com. '[I'm] literally sleeping four hours a night and feeling great.'New Horizons will make its closest to Pluto at 7:49 a.m. EDT tomorrowPrincipal investigator, Alan Stern, has spent 15 years working on missionPluto has taught us 'that our view of the solar system is wrong', said SternDwarf planet is thought to be a relic left from formation of the solar systemFirst close-up images will be sent back to Earth on Wednesday morning 
 Question:They also plan to measure the temperature and pressure in _'s nitrogen-rich atmosphere and determine how much gas is escaping into space.

Pluto