Skydiving onto Venus
QI WHY WILL DAVINCI JETTISON ITS PARACHUTE SO QUICKLY INTO VENUS’ ATMOSPHERE? WON’T THIS RESULT IN LESS TIME TO COLLECT DATA AND IMAGES? Steven Portalupi Newmarket, New Hampshire
A IVenus and its massive atmosphere present an incredibly challenging environment for any in situ probe mission. The planet’s surface temperature is approximately 860 degrees Fahrenheit (460 degrees Celsius) thanks to the dense CO2 atmosphere, which also creates a surface pressure 90 times greater than Earth at sea level.
Sulfuric acid clouds exist roughly 25 to 43 miles (40 to 70 kilometers) above the surface in a thick layer. When the DAVINCI descent sphere spacecraft (DS) jettisons its main parachute approximately 32 minutes into the descent — around 24 miles (39 km) above the surface — the temperature will already be 304 F (153 C).
This truly hellish environment presents challenges that other planetary probes don’t have to face. Trying to build a parachute that could survive these conditions would be risky and expensive. Thus, DAVINCI employs fixed drag plates to slow its descent after jettisoning the parachute. The thick venusian atmosphere also helps because the descent is more like settling into a fluid than falling through air.
It’s true that by cutting the parachute loose, the DS will spend less time in Venus’ lower atmosphere. But in many ways, this is an advantage because the craft spends less time exposed to the harsh conditions there. If the DS remained longer on the parachute, it would need to be designed to absorb more heat to keep the internal science instruments cool and have larger batteries to keep the craft operating longer through the descent. This would increase the weight, which makes it even more challenging to build a parachute to support it!
To ensure DAVINCI meets its science objectives, the DS makes use of state-of-the-art chemistry instruments
and telecommunications systems that can sample the atmosphere every 500 feet (150 meters) of descent and take near-infrared images every few seconds. The DS will transmit this data to its companion craft in venusian orbit, the Carrier Relay Imaging Spacecraft (CRIS), before reaching the surface. So, in the short hour that DAVINCI will spend in Venus’ atmosphere, it will acquire groundbreaking measurements and images far beyond what any previous mission has managed.
Colby Goodloe DAVINCI Descent Sphere Lead Engineer, NASA Goddard Space Flight Center, Greenbelt, Maryland, on behalf of the DAVINCI Project
QI I’VE READ THAT THE STRENGTH OF A NEUTRON STAR’S MAGNETIC FIELD IS GREATER THAN ANY OTHER FOUND IN THE UNIVERSE. WOULDN’T A SUPERMASSIVE BLACK HOLE HAVE A STRONGER ONE? Patrick Clough Wichita, Kansas
A IThe answer to this question is quite complicated. There is a so-called no-hair theorem, which basically states that only three observable parameters can be determined for each black hole: its mass, electric charge, and rotation. The hair here is a metaphor for all other possible parameters, including magnetic fields, which disappear inside the black hole and become inaccessible to scientists. So, a black hole by itself does not have any measurable magnetic field.
However, any matter that accretes onto a black hole could be magnetized. In this case, the magnetic field will become stronger as the matter approaches the black hole and is compressed. So, magnetic fields do exist around supermassive black holes, but their source is the accretion disk, not the black hole itself.
For example, when the Event Horizon Telescope collaboration imaged the supermassive black hole in M87, they observed radio waves that were polarized by the magnetic field in the surrounding accretion disk. The team estimated the magnetic field strength to be between two to 50 times stronger than Earth’s magnetic field. But that is a tiny magnetic field compared with the magnetic fields around pulsars and magnetars. In particular, magnetars retain the strongest magnetic fields in the universe, at a thousand trillion times stronger than Earth’s field.
Andrei Igoshev Astronomy Research Fellow, University of Leeds, Leeds, United Kingdom
QI AT WHAT RATE IS THE MOON MOVING AWAY FROM EARTH? WHAT KINDS OF CONSEQUENCES WILL OUR PLANET SEE AS OUR SATELLITE MOVES FARTHER AWAY? Eliot H. Ginsberg Riverview, Florida
A ILet’s first look at why the Moon is moving away from us. It boils down to one of Newton’s laws: conservation of angular momentum. As the Moon’s gravity pulls on Earth, it produces tidal forces that make the oceans bulge and cause Earth’s rotation to lose momentum. Slowing Earth’s rotation in turn speeds up the Moon’s orbit, which must expand to conserve the total momentum of the Earth-Moon system.
The Moon is moving away from Earth at about 1.49 inches (3.78 centimeters) per year. And as it moves away, its orbital period increases and Earth’s rotation slows down. Looking at the average rate of retreat over the last 4 billion years, it should take about 50 billion years before the Moon takes as long to complete one orbit as Earth takes to complete one rotation.
At this point, Earth will be tidally locked to the Moon, which will always sit above the same point on the planet. Only half of the planet will ever see the Moon. The Moon’s changing impact on our tides would also cease, though there would still be some time-dependent tides, thanks to the Sun. The Sun-Earth tidal tug-of-war would eventually reverse the Earth-Moon process, bringing the Moon steadily closer to Earth until our planet’s gravity tore it apart.
Of course, in 50 billion years, the Sun will have long since become a white dwarf. (This will happen in 10 billion years.) And, in all likelihood, Earth and the Moon will not survive the Sun settling into its twilight years.
Caitlyn Buongiorno Associate Editor