Today is the equinox, that day of awesome geometric alignments, when the Sun crosses the equator, and when for a moment both the north and south pole are illuminated. Let’s celebrate by talking about how Venus might have once been capable of supporting life, and how Japan continues dropping things on asteroids.



The Equinox

Artist’s representation of Venus with water. Credit: NASA

Was Venus habitable?

The separation image of the 2nd target marker, TM-C!

Separation time: 2019/9/17 at 01:24 JST
Altitude: 1km

This is an overlay of images taken every 4s (for ~1min) while the spacecraft ascends at 11cm/s. TM descent speed is still almost zero. (
JAXA, Chiba Inst. Tech & collab)

Japan’s Hayabusa 2 mission to Ryugu


Happy Equinox everyone! Last night, at 1:50am Eastern time, the Sun passed directly over the Earth’s equator. At that moment, nothing magical happened, but it is still a neat geometry, with Sun beams hitting both poles for a single moment. From this point forward, parts of the north pole will begin to not get sunlight, and parts of the south pole will begin to actual days for the first time in 6 months. For many, this is a holiday that marks the turning of the seasons, and I’m not going to lie, Halloween decorations have started to make their yearly journey into my house, where they will remain until at least Thanksgiving, because that’s just how we roll. In this video, you can see how over the course of a year, the way the sun illuminates changes. This changing angle of sunlight is actually do to our Earth’s tilt relative to the Sun, and our motion around that sun. Throughout the current year, our planet will keep it north pole politely pointed toward the north star, Polaris.  When the Sun is between the Earth and Polaris, we have northern Summer. When the Earth is between Polaris and the Sun, we have Northern winter. Planetary tilt, not distance from the sun or anything else, determines seasons. Jupiter, is only tilted 3.13 degrees doesn’t have major seasonal variations, while Uranus, which is tilted almost on its side at 98 degrees, has massive season differences between its hemispheres. So, when you are asked the reason for the season, remind people that setting all else aside, axial tilt is the reason for winter, spring, summer, and fall.

The weather we experience today on earth is very different from what was experienced during the ice age, or even during the dark ages! Over time, a variety of factors have changed our world’s climate, and in the past, some of those changes were driven by volcanoes, impacts, and other out of this world events. This isn’t true of just the Earth. It is often noted that Mars once supported massive oceans and a thicker atmosphere. Well, in a new release which appears to be the very last release of the European Planetary Science Congress, we get word that even Venus may once have been a wet and potentially habitable world….And this wasn’t a temporary thing. According to new models, Venus may have maintained stable temperatures maxing out at just 50 degrees Celsius for 3 billion years. That is just 122F, or what is some might call a nice summer day in Phoenix Arizona. These simulations were based on models that assumed various amounts of surface water existed on Venus 4.2 billion years ago. Running these models forward, they found that every model allowed Venus to maintain its habitable environment until a massive and catastrophic out-gassing event occurred just 700 to 750 million years ago. On our own planet, life was just starting to evolve 700 to 800 million years ago, with the emergence of the first flagella-waving protists, but, if life was faster to evolve on Venus, it’s possible that the destruction of that world’s environment was the greatest extinction event our solar system as thus far known.

According to project scientist Michael Way, “Something happened on Venus where a huge amount of gas was released into the atmosphere and couldn’t be re-absorbed by the rocks. On Earth we have some examples of large-scale out-gassing, for instance the creation of the Siberian Traps 500 million years ago which is linked to a mass extinction, but nothing on this scale. It completely transformed Venus.” We know from radar imaging of Venus that this world has vast volcanic structures, and some papers have postulated that at some point in Venus’s past, build internal heat produced a massive, planet wide episode of volcanism. That single event, or one like it, just might have ruined a once habitable world forever.

And from one lifeless world to another, we turn to Ryugu and the Hayabusa2 spacecraft that is exploring it. Last week, Hayabusa2 dropped 2 target markers on the surface of this little asteroid in preparation s to send its 3rd and final rover. JAXA will continue to observe the site where these target markers landed through today, and will use this data to plan their as-yet-unscheduled rover landing. Deployment of Minerva II will be Hayabusa2’s last major milestone before it heads back toward Earth in November, and flings its rocky samples at Australia in December 2020.

And that rounds out our science for today. 

We do have a quick announcement. A week from Saturday the world is invited to celebrate International Observe the Moon Night. That October 5, astronomy clubs, museums, and Luna-loving lunatics will be gathering together to look up. If you are near Tucson, Arizona, you are invited to join me at the Flandrau Center, where I’ll be giving a free public talk at 7pm in the planetarium.

Thank you all for listening. The Daily Space is produced by Susie Murph, and is a product of the Planetary Science Institute, a 501(c)3 non profit dedicated to exploring our Solar System and beyond. We are made possible through the generous contributions of people like you. If you would like to learn more, please check us out on

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