On April 22, NASA will post about 200 images across nearly 100 different social media channels that capture the breadth of the agency’s 24-hour-a-day work to study Earth. The images were captured during the week of March 27, but have been assembled chronologically to tell a story of a “day in the life” of NASA’s Earth science work. The time-stamped posts -- hashtagged #24Seven -- will begin publishing at 12:01 a.m. EDT and will continue throughout the day.

Share your posts on Twitter or Instagram with the hashtag #24Seven, or on our Facebook Event page.We know we aren’t the only people working to safeguard and understand our home planet. As you celebrate Earth Day, we’re asking you to share on social media what you’re doing to mark the day and celebrate our fragile home in space.

Share your posts on Twitter or Instagram with the hashtag #24Seven, or on our Facebook Event page.

How can I take part?

Millions of people will take time out of their day this April 22 to do their part to make Earth a better place. Others will mark the day by spending it outside, celebrating the beauty, ruggedness and life-giving elements that make Earth our home in the solar system.

Take a picture or a short video of whatever Earth-focused activity you are doing on Earth Day and post it on social media with the hashtag #24Seven. Pictures and videos can be posted to Twitter, Instagram and to the official NASA Facebook Event page.

Begin posting at 6 a.m. EDT on April 21 – which marks the beginning of Earth Day on the international date line at Samoa and Christmas Island, Kiribati – and continue posting until 8 a.m. EDT on April 23, which marks the end of Earth Day on the other side of the international date line at Baker Island.

Fritz Leiber is better known for his fantasy and SF-fantasy, but he could write hard-SF too. A fine example is his 1962 story, “The Snowbank Orbit”, the title of which alludes to World War II tales of pilots surviving bailouts without parachutes by plunging into snow-drifts. Five spacecraft, racing towards Uranus at 100 miles per second with empty tanks, intend a fiery plunge through the planet’s atmosphere to brake into orbit. The rest of that story I will leave to the interested reader (available here) but the idea of aerobraking into orbit around a distant Planet Nine is worth discussing.

Presently we know very little about Telisto – the mellifluous name suggested for Planet Nine by physicist Lorenzo Iorio [1] which I’ll use for convenience. Brown & Batygin [2] suggest an orbit averaging about 700 AU and a mass of at least 10 Earth masses. The mass could be somewhat higher, though certainly not of the order of a Saturn-mass as its infra-red glow would’ve been seen by earlier surveys. Modelling [3] suggests a 10 Earth-mass planet, with a substantial hydrogen-helium envelope, could be as ‘warm’ as 50 K – about 40 degrees warmer than the ~10 K from sunlight alone. A range of compositions were modelled. A Super-Earth, an Ice-Giant (like Uranus/Neptune) and a miniature version of Jupiter/Saturn are all possible. Some cosmogonic simulations [4] suggest a Neptune like object is likely to have been flung from amongst the other giant planets during their formation, so it seems the most likely option.

A Neptune-like Telisto would then be an ice-wrapped rocky core wrapped in a layer of captured hydrogen/helium mixture. It’s likely that hydrogen will be depleted from its atmosphere by some fraction being chemically bound and mixed with its core, so helium will be a higher fraction of the atmosphere, as appears to be the case for Neptune. If the atmosphere is a small fraction of Telisto’s mass, then it’s possible it will have an icy surface or even a liquid water ocean under a hydrogen atmosphere via its greenhouse effect trapping the planet’s internal heat. In that case Telisto will be very interesting from an astrobiological perspective, though the energy sources available to sustain life are impossible to quantify at present.

Deep Space Propulsion

Given sufficient motivation we’ll send a probe and eventually follow in person. Getting there will be a challenge. At the present 3.5 AU/year of “Voyager 1” the journey would take 200 years. Leiber’s 100 miles per second would get a probe there in 20 years, which might be acceptable if the probe has a compelling secondary mission it can pursue during the long cruise phase. Long baseline telescopic observations might be sufficiently attractive to combine the two. A flyby at 100 miles per second is probably too quick to provide sufficient science return for the investment, so stopping will be required.