Clouds on the [New] Horizon

Cecilia Santostefano

Since its discovery in 1930, it has been difficult for astronomers to observe Pluto because of its small size. NASA has utilized telescopes like the Hubble to learn about Pluto in the past, but the latest mission involves the New Horizons spacecraft. Images reveal the planet covered in water-ice mountains, plains of frozen nitrogen, and blue skies may also have clouds.[1]

Following the cancellation of the Pluto Fast Flyby and the Pluto Kuiper Express, the National Aeronautics and Space Administration (NASA) developed another interplanetary space probe to explore Pluto. This spacecraft was named New Horizons. While planets like Earth and Venus are classified as “rocky planets,” Pluto and its largest moon Charon are categorized as “ice dwarfs.”[2] This is because they have solid surfaces, but unlike Earth, Venus, and other terrestrial planets, a large portion of their mass is icy material.[3]

The mission to Pluto addressed three objectives: (1) what Pluto, Charon, and the other four moons look like, are made of, and the nature of Pluto’s atmosphere, (2) variability in temperature to track activity, and (3) the radii, masses, densities, and orbits of Pluto and the other moons.[4] To reach its objectives, the spacecraft was equipped with a radioisotope thermoelectric generator (RTG) to measure temperature and a long-range reconnaissance imager (LORRI) for high resolution images. New Horizons launched from Florida back in 2006 and reached Pluto in 2015. As of October 2016, New Horizons completed its Pluto flyby.

During the flyby in July 2015, New Horizons obtained images of a primarily cloud-free Pluto.[5] At an annual meeting of the American Astronomical Society’s planetary scientists in October, principal researcher Alan Stern presented images of seven separate cloud candidates that imply clouds form at dusk and dawn on Pluto.[6] Not a vast amount is known about this planet, but scientists are already aware that the level of brightness indicates surface activity on the planet. Scientists are also already aware of layers of hazes (which are not clouds) up to 200 km above the surface. This evidence now suggests condensation.[7] The seven cloud candidates are, however, different than the clouds found on Earth because they do not appear layered.[8]  Stern reported “. . . individual, discrete potential cloud features” are seen.[9] Since the potential clouds are so close to Pluto’s surface, nothing can be confirmed without further investigation. Stern informed fellow scientists confirmation requires   “. . . more instrumentation and more time.”[10]

New Horizons wrapped up its Pluto flyby in mid-October and is continuing to other regions in the Kuiper Belt. The mission was extended over the course of summer 2016, and the spacecraft is set to continue through the Kuiper Belt in search of information as to how Pluto fits into the solar system.


[1] Kenneth Chang, Pluto May Have Clouds, New Data Indicate, NY Times, (Oct. 18, 2016),

[2] Brian Dunbar, New Horizons: The First Mission to the Pluto System and the Kuiper Belt, National Aeronautics and Space Administration, (Aug. 24, 2015),

[3] Id.

[4] Science Objectives, Space Flight 101, (2016),

[5] Chang, supra note 2.

[6] Alan Yuhas, Nasa Findings hint of clouds on Pluto during New Horizons mission, The Guardian, (Oct. 18, 2016, 5:48 PM),

[7] Id.

[8] Id.

[9] Chang, supra note 1.

[10] Yuhas, supra note 6.