Venus – the forgotten planet

Mars inspires dreams of humans spreading into the Solar System, Saturn’s beauty mesmerises all those who see it for the first time and Jupiter marvels with its size and huge storms and I’m not even going to mention Pluto here, yet poor old Venus gets a big ol’ ignoring even though is the most reported “UFO” out there as seen with the naked eye. So this article takes a look at Venus and what we humans have done to try and understand this planet a little more. Venus has often been thought as the Earth’s twin, it’s about the same size, it has an atmosphere and it often dominates the evening or dawn so has been the object of human attention for many thousands of years. The only current mission whizzing around Venus is Akatsuki, Venus Climate Orbiter, which is a Japanese probe that was intended to look at Venus’ atmosphere and understand the flows going on in the atmosphere. The plan was to map the clouds and the constituents. The instruments included 4 cameras and and an ability to measure the vertical structure of the clouds. The mission was to complement the European Venus Express mission, which operated successfully in a polar orbit for 9 years.

Artist’s impression of Akatsuki (Credit: JAXA)

It was launched on 20 May 2010 on a Japanese H-IIA 202 rocket. The launch went well with the rocket performing as planned and the spacecraft separating without a hitch. By December the plan was to get the spacecraft into orbit around Venus but things did not go to plan and Akatsuki missed the orbit insertion. The problem was eventually thought to be damage to a thruster nozzle of the orbit manoeuvre engine. Subsequent tests confirmed that this engine wasn’t producing the amount of thrust is was supposed to, only about one ninth of the expected amount. Because this engine was not much use, JAXA decided to use a different engine to try and get the spacecraft into orbit, the reactor control system (RCS) or attitude control thruster. The engine burn was successful and in January 2012 Akatsuki set off to intercept Venus in 2015. On 9 December 2015 JAXA confirmed that a second attempt at entering orbit had been successful with the orbital parameters being between 400km and 440,000km in altitude and a period of 13 days and 14 hours. This orbit is inclined at about 3 degrees from the orbital plane of the planet and is in the direction of rotation. Even if it hasn’t gone into exactly to plan, the manoeuvre put Akatsuki in a position where it can be used. By April 2016 the instruments were ready to go and the mission was finally begun.

Image from 72,000km during first past in 2010 (Credit: JAXA)

The instruments onboard the spacecraft include 1 micron IR camera, called IR1. The purpose of this camera is to image the day side of Venus. The camera is designed to look at a number of wavelengths that will help examine both the surface and aspects of the atmosphere. The second instrument is a 2 micron IR camera, called R2. This camera is focused on understanding what is happening in the in the 35km – 50km altitude in the atmosphere. The third instrument is an ultraviolet imager that is designed to measure the scattering of UV light from the cloud tops at around 65km in altitude. The fourth instrument in the long wave IR camera or LIR. This camera specialises in 8-12 micron wavelengths to measure the temperature of the cloud tops. The fifth instrument is called the Lightning and Airglow Camera (LAC) and its job is to capture lightning on the night side of the planet. The final instrument is simply called Radio Science (RS) and basically looks at radio waves to determine the vertical structure of the atmosphere.

1 December 2015 test image from 1.1 million km (Credit: JAXA)

Despite the problems it had with the orbit insertion, the spacecraft has discovered some useful things, including the existence of an equatorial jet, which has not been observed before. The atmosphere of Venus is very thick and it has almost constant high wind speeds, the clouds range from about 45km to 70km in altitude. The wind speed at low latitudes has been estimated at about 300kmh with slightly slower speeds the further from the equator. Another feature discovered by the spacecraft was a large bow shaped object stretching from the North to South over about 10,000km. This shape remained in place for 4 days of observation without being affected by the prevailing wind. The finding was that these sorts of structures are probably caused by waves from turbulence at lower levels. The waves propagate North and South and pop at at the top of the clouds at about 65km. This discovery helped scientists determine that they can work out a lot of what’s going on at the surface by observations of the cloud tops.

A localised vortex near the cloud base in Mar 2017 (Credit: JAXA)

Unlike Mars, there’s not a lot planned for Venus in the future so we might have to be content with Akatsuki for the time being. Akatsuki, despite the initial problems, has advanced our understanding of Earth’s angry twin.