Exoplanets between 2 and 4 times the size of Earth may feature water as a large component in their make-up, with many comprising perhaps up to 50% water by weight (by contrast, Earth has just 0.02% water content by weight).
This is the conclusion drawn by an international team of researchers who have being pouring (pun intended) over data from the Kepler Space Telescope and the Gaia mission gathered on the 4,000+ exoplanets discovered thus far, many of which tend to fall into two categories: those with the planetary radius averaging around 1.5 that of the Earth, and those averaging around 2.5 times the radius of the Earth.
It was a huge surprise to realise that there must be so many water-worlds. We have looked at how mass relates to radius, and developed a model which might explain the relationship. The model indicates that those exoplanets which have a radius of around x1.5 Earth radius tend to be rocky planets (of typically x5 the mass of the Earth), while those with a radius of x2.5 Earth radius (with a mass around x10 that of the Earth) are probably water worlds. Our data indicate that about 35% of all known exoplanets which are bigger than Earth should be water-rich.
– Dr. Li Zeng of Harvard University, lead researcher on the study
The teams findings could have major implications for our understanding of the composition of Earth-sized exoplanets. However, if the team’s conclusions are correct, it doesn’t necessarily mean these are especially balmy places. Many orbit so close their parent stars their surface temperatures are liable to be in the 200-500o Celsius range (392-932oF), so the water on them is liable to be very different to how we find it on Earth, existing as saturating vapour in the atmosphere, then a world-girdling warm ocean with ice under increasing pressure below it, wrapped around a sold core.
The beauty of the model is that it explains just how composition relates to the known facts about these planets, and offers insight into how they were formed – most likely in a similar manner to the cores of the giant planets in our own solar system.
With a new generation of Earth-based telescopes capable of peering at distant planets currently gaining remarkable optical updates (such as ESO’s Very Large Telescope) or under construction (the Giant Magellan Telescope or GMT), not to mention the James Webb Space Telescope and the Transiting Exoplanet Survey Satellite (see below for more in this), the hope is that the findings presented by the team will soon be backed-up with hard data as atmospheres around these distant worlds are properly characterised.
TESS Starts Work
TESS, the Transiting Exoplanet Survey Satellite launched on April 16th, 2018, has started its primary mission – taking over from the ailing Kepler mission in locating exoplanets. This initial primary mission will last for 2 years, in which it is anticipated TESS will pay particular attention to the 200,000 brightest stars around us in the hope of detecting planetary bodies in orbiting them. It will do this using the transit method of observation – looking for dips in the brightness of stars which might indicate the passage of an orbiting planet between the star and the telescope.
The first data gathering element of the mission commenced on July 25th, and will continue through most of August before the data is transmitted by to Earth from TESS’s unique orbit, a “2:1 lunar resonant orbit“, which allows the craft to remain balanced within the gravitational effects of the Moon and Earth, providing a stable orbital regime which should last for decades.
As a part of the mission, the TESS science team aims to measure the masses of at least 50 small planets whose radii are less than four times that of Earth, offering the opportunity to characterise their likely structure and composition. Many of TESS’s planets should be close enough to our own that, once they are identified by TESS, scientists can zoom in on them using other telescopes, to detect atmospheres, characterise atmospheric conditions, and even look for signs of habitability.
In this latter regard, TESS will pave the way for detailed studies of candidate exoplanets by the James Webb Space Telescope (JWST), now scheduled for launch in 2021. While TESS cannot look for atmospheric or other signs of life on the distant worlds it locates, JWST will be able to do just that, which could see the 2020s a decade of remarkable extra-solar planetary discoveries.
SpaceX Bullish on Meeting NASA Schedule
At the start of August 2018, I wrote about the first nine astronauts selected to fly the initial missions of the Boeing CST-100 Starliner and the SpaceX Crew Dragon to and from the International Space Station as a part of NASA’s Commercial Crew Programme. However, alongside the announcement, NASA also pushed back the dates of the initial test flights for the two vehicles, with a warning there could be further slippage.
SpaceX has now given a bullish projection that they will meet the new time frames specified by NASA for the initially uncrewed test flight of Crewed Dragon (November 2018) the crewed test flight (April 2019).
Predicting launch dates could make a liar out of the best of us. I hope I am not proven to be a liar on this one … We want to make sure not only that we get these folks up and back safely but that that’s reliable and a mission that we conclude. We want to hit all the boxes do everything we need to do, to demonstrate that this vehicle is capable of taking astronauts up from US soil as often as NASA will allow us.
Gwynne Shotwell, SpaceX President, speaking on August 14th
The rescheduling of the SpaceX flights came as a result of a redesign requirement for the composite over-wrapped pressure vessels (COPVs) used to store helium in the propellant tanks on the Falcon 9. The redesign was called for after investigations revealed the failure of COPV during the pre-launch fuelling of a Falcon 9 in September 2016 to be the cause of the catastrophic loss of vehicle and payload. This redesign must be completed and certified for human flight before NASA will allow astronauts to fly on Crew Dragon.
In addition, the COPV was seen as indicative of the risky approach SpaceX take to their Falcon 9 launches. Traditionally, for a crewed flight, the last thing into a launch vehicle is the crew: they board only when all else is ready to go, and the vehicle is fully fuelled, allowing it to lift-off just as soon as the final pre-flight checks are completed. For Falcon 9 launches however, SpaceX use what is called a “load and go” approach, fuelling the vehicle in the last 35 minutes before launch, with the crew already in their capsule – and so at risk should anything go wrong during the fuelling process.
“Load and go” minimises the amount of vaporisation that can occur with super-cold propellants if stood for an extended period on the launch pad without proper refrigeration, requiring both a means to vent the vapour and to “top up” the fuel. While SpaceX had indicated they could adopt to fuelling the vehicle ahead of the crew boarding, “load and go” has remained the preferred approach, and one subject to a lengthy NASA safety review.
On August 17th, 2018, that review concluded SpaceX can use “load and go” for crewed flights to the ISS – providing the company can meet additional verification and demonstration tests ahead of April 2019 test flight. These tests include completing five “crew loading demonstrations” using the approach as if a crew were sitting atop a Falcon 9 awaiting launch.
A First Look at Lockheed’s Deep Space Living Module
On Thursday, August 16th, Lockheed Martin presented a first look at their vision of the crew module element of NASA’s Lunar Orbit Platform-Gateway (LOP-G). Intended to orbit the Moon from around 2024, LOP-G is being promoted as providing both a “stepping stone” for humans to return to the Moon, and as the “launch point” for Mars and other destinations.
Just 6.7 metres (22 ft) in length and 4.6 metres (15 ft) in diameter, the unit is essentially a re-working of their Donatello Multi-Purpose Logistics Module, the third unit in a series originally designed to ferry supplies to the ISS on the space shuttle, only the first two of which were actually used. In its new role, the unit is intended to be both a working and living space for four people between 30 and 60 days at a time. Lockheed acknowledge the space is so limited, crews will have to live “RV style” – packing away the meal table and other elements in order to make room to sleep, then packing their sleeping gear away to make room to work. Hardly an approach geared towards crew comfort or convenience.
Classic Images for a Classic
In June 2018, as a part of the celebrations of NASA’s 60th anniversary, a special concert was held at the Kennedy Centre for the Performing Arts in Washington, DC. One of the pieces featured by National Symphony Orchestra Pops, led by conductor Emil de Cou, was a rendition of Claude Debussy’s hauntingly beautiful Claire de Lune.
Accompanying it was a film put together by the Scientific Visualisation Studio at Goddard Space Centre. These are the folk responsible for producing visualizations, animations, and images designed to help promote a greater understanding of Earth and Space Science research activities at NASA and within the academic research community supported by NASA – and I’ve featured a number of their You Tube videos in my Space Sunday updates.
The film features an unfolding lunar “day” using images captured by NASA’s Lunar Reconnaissance Orbiter (LRO) which were used to build a 3D model of the Moon’s surface which an accurate height elevation and using modelled light that directly correlated to the angle and intensity of the Sun’s light falling across the Moon.
The result is a stunning video, perfectly reflecting the contemplative nature of Debussy’s 1905 composition and featuring some of the Moon’s most well-known features. These include the Apennine and Caucasus mountain ranges, Copernicus crater and the Aristarchus plateau, all at sunrise and sunset, the North and South poles at noon, and the fully illuminated lunar farside through the day. Enjoy!