President Barack Obama makes a phone call with the crew of the Space Shuttle Discovery and the International Space Station from the Oval Office, March 3, 2011. Listening in the background are, from left: Ted Wackler, Acting Chief of Staff, Office of Science and Technology; Damon Wells, Assistant Director for Aeronautics and Space, Office of Science and Technology; and NASA Administrator Charles Bolden. (Official White House Photo by Samantha Appleton) This photograph is provided by THE WHITE HOUSE as a courtesy and may be printed by the subject(s) in the photograph for personal use only. The photograph may not be manipulated in any way and may not otherwise be reproduced, disseminated or broadcast, without the written permission of the White House Photo Office. This photograph may not be used in any commercial or political materials, advertisements, emails, products, promotions that in any way suggests approval or endorsement of the President, the First Family, or the White House.

President Barack Obama talks with the crews of the Space Shuttle Atlantis and the International Space Station during a phone call in the Oval Office, Friday, July 15, 2011, in Washington. (Official White House Photo by Pete Souza)

President Barack Obama poses with Apollo 11 astronauts, from left, Buzz Aldrin, Michael Collins, and Neil Armstrong, Monday, July 20, 2009, in the Oval Office of the White House in Washington, on the 40th anniversary of the Apollo 11 lunar landing. Photo Credit: (NASA/Bill Ingalls)

STS-133 Commander Steven Lindsey, far left, presents a montage to President Barack Obama as crew members Michael Barratt, Pilot Eric Boe, Nicole Stott, and Stephen Bowen look on during a visit to the Oval Office in the White House, Monday, May 9, 2011, in Washington. Also in attendance but not seen, was Mission Specialist Alvin Drew. Photo Credit: (NASA/Paul E. Alers)

President Barack Obama meets with Apollo 11 astronauts Michael Collins, seated left, Buzz Aldrin, center, Carol Armstrong, widow of Apollo 11 commander, Neil Armstrong, and NASA Administrator Charles Bolden, Tuesday, July 22, 2014, in the Oval Office of the White House in Washington, during the 45th anniversary week of the Apollo 11 lunar landing. Photo Credit: (NASA/Bill Ingalls)

STS-133 Commander Steven Lindsey, far left, presents a montage to President Barack Obama as crew members Michael Barratt, Pilot Eric Boe, Nicole Stott, and Stephen Bowen along with NASA Administrator Charles Bolden, far right, look on during a visit to the Oval Office in the White House, Monday, May 9, 2011, in Washington. Also in attendance but not seen, was Mission Specialist Alvin Drew.Photo Credit: (NASA/Paul E. Alers)

Marshall's eighth Center Director Dr. Jerroll W. Littles (1996-1998) and his wife are pictured with President Bill Clinton in the Oval Office of the White House following the presentation of the Presidential Rank Award for Distinguished Service. Other NASA honorees and their spouses are also pictured.

jsc2017e049162 (April 24, 2017) --- Flight Director Brian Smith, Capcom Astronaut Jessica Meir along with Astronaut Jeff Williams monitor activities in Mission Control as President Donald Trump, First Daughter Ivanka Trump and NASA astronaut Kate Rubins make a special Earth-to-space call from the Oval Office to personally congratulate NASA astronaut Peggy Whitson for her record-breaking stay aboard the International Space Station. (Photo Credit: NASA/Robert Markowitz)

jsc2017e049163 (April 24, 2017) --- Flight Director Brian Smith, Capcom Astronaut Jessica Meir along with Astronaut Jeff Williams monitor activities in Mission Control as President Donald Trump, First Daughter Ivanka Trump and NASA astronaut Kate Rubins make a special Earth-to-space call from the Oval Office to personally congratulate NASA astronaut Peggy Whitson for her record-breaking stay aboard the International Space Station. (Photo Credit: NASA/Robert Markowitz)

jsc2017e049157 (April 24, 2017) --- Flight Director Brian Smith, Capcom Astronaut Jessica Meir along with Astronaut Jeff Williams monitor activities in Mission Control as President Donald Trump, First Daughter Ivanka Trump and NASA astronaut Kate Rubins make a special Earth-to-space call from the Oval Office to personally congratulate NASA astronaut Peggy Whitson for her record-breaking stay aboard the International Space Station. (Photo Credit: NASA/Robert Markowitz)

jsc2017e049158 (April 24, 2017) --- Flight Director Brian Smith, Capcom Astronaut Jessica Meir along with Astronaut Jeff Williams monitor activities in Mission Control as President Donald Trump, First Daughter Ivanka Trump and NASA astronaut Kate Rubins make a special Earth-to-space call from the Oval Office to personally congratulate NASA astronaut Peggy Whitson for her record-breaking stay aboard the International Space Station. (Photo Credit: NASA/Robert Markowitz)

jsc2017e049161 (April 24, 2017) --- Flight Director Brian Smith, Capcom Astronaut Jessica Meir along with Astronaut Jeff Williams monitor activities in Mission Control as President Donald Trump, First Daughter Ivanka Trump and NASA astronaut Kate Rubins make a special Earth-to-space call from the Oval Office to personally congratulate NASA astronaut Peggy Whitson for her record-breaking stay aboard the International Space Station. (Photo Credit: NASA/Robert Markowitz)

jsc2017e049159 (April 24, 2017) --- Flight Director Brian Smith, Capcom Astronaut Jessica Meir along with Astronaut Jeff Williams monitor activities in Mission Control as President Donald Trump, First Daughter Ivanka Trump and NASA astronaut Kate Rubins make a special Earth-to-space call from the Oval Office to personally congratulate NASA astronaut Peggy Whitson for her record-breaking stay aboard the International Space Station. (Photo Credit: NASA/Robert Markowitz)

jsc2017e049155 (April 24, 2017) --- Flight Director Brian Smith, Capcom Astronaut Jessica Meir along with Astronaut Jeff Williams monitor activities in Mission Control as President Donald Trump, First Daughter Ivanka Trump and NASA astronaut Kate Rubins make a special Earth-to-space call from the Oval Office to personally congratulate NASA astronaut Peggy Whitson for her record-breaking stay aboard the International Space Station. (Photo Credit: NASA/Robert Markowitz)

jsc2017e049156 (April 24, 2017) --- Flight Director Brian Smith, Capcom Astronaut Jessica Meir along with Astronaut Jeff Williams monitor activities in Mission Control as President Donald Trump, First Daughter Ivanka Trump and NASA astronaut Kate Rubins make a special Earth-to-space call from the Oval Office to personally congratulate NASA astronaut Peggy Whitson for her record-breaking stay aboard the International Space Station. (Photo Credit: NASA/Robert Markowitz)

jsc2017e049160 (April 24, 2017) --- Flight Director Brian Smith, Capcom Astronaut Jessica Meir along with Astronaut Jeff Williams monitor activities in Mission Control as President Donald Trump, First Daughter Ivanka Trump and NASA astronaut Kate Rubins make a special Earth-to-space call from the Oval Office to personally congratulate NASA astronaut Peggy Whitson for her record-breaking stay aboard the International Space Station. (Photo Credit: NASA/Robert Markowitz)

Photo by Voyager 2 (JPL) During August 16 and 17, 1989, the Voyager 2 narrow-angle camera was used to photograph Neptune almost continuously, recording approximately two and one-half rotations of the planet. These images represent the most complete set of full disk Neptune images that the spacecraft will acquire. This picture from the sequence shows two of the four cloud features which have been tracked by the Voyager cameras during the past two months. The large dark oval near the western limb (the left edge) is at a latitude of 22 degrees south and circuits Neptune every 18.3 hours. The bright clouds immediately to the south and east of this oval are seen to substantially change their appearances in periods as short as four hours. The second dark spot, at 54 degrees south latitude near the terminator (lower right edge), circuits Neptune every 16.1 hours. This image has been processed to enchance the visibility of small features, at some sacrifice of color fidelity. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications. (JPL Ref: A-34611 Voyager 2-N29)

Voyager II Imagery; Neptune. This bulls-eye view of Neptune's small dark spot (D2) was obtained by Voyager 2's narrow-angle camera , when Neptune was within 1.1 million km (680,000 miles) of the planet. The smallest structures that can be seen are 20 km (12 miles) across. This unplanned photograph was obtained when the infrared spectrograph was mapping the the highest-resolution view of the feature taken during the flyby. Banding surrounding the feature indicates unseen strong winds, while structues within the bright spot suggest both active upwelling of clouds and rotation about the center. A rotation rate has not yet been measured, but the v-shaped structure near the right edge of the bright area indicates that the spot rotates clockwise. Unlike the Great Red Spot on Jupiter, which rotates counterclockwise, if the D2 spot on Neptune rotates clockwise, the material will be descending in the dark oval region. The fact that infrared data will yield temperature information about the region above the clouds makes this observation especially valuable. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applicaitons. (JPL ref: P-34749 Voyager N-71) taken during the flyby. Banding surrounding the feature indicates unseen strong winds, while structures within the bright spot suggest both active upwelling of clouds and rotation about the center. A rotation rate has not yest been measured, but the Vv-sphped