Life Forms On Venus? Probably Not
In a recent paper, a highly respected and pioneering planetary scientist in Russia has suggested that images from the Venera-13 lander might show life forms on the surface of Venus. Dr. Leonid Ksanfomality did important work on the spectroscopy of Venus and Mars from spacecrafts in the 1970s and 1980s, and he was the first to discover that lightning was common in the atmosphere of Venus.
His latest paper has raised eyebrows throughout the planetary science community: "Venus as a Natural Laboratory to Find Life at High Temperature: Events on the Planet". In it, he claims three particular examples of mysterious objects: a moving disk shaped form, a "scorpion" shaped object, and a moving black object. I would like to present an alternative theory for these objects, which I believe is more likely. First a quick review of the camera and telemetry system of Venera-13. A broader discussion of that mission can be found here: http://www.mentallandscape.com/V_Venera11.htm
Nearing Venus, on Feb 28, 1982, the massive Venera-13 separated into a landing vehicle and a large flyby spacecraft. These encountered the planet on March 1, where the lander set down at 03:57:21 UTC. It drilled into the surface to analyze the rocks, and several minutes later, a cycloramic camera began to scan the surface through a thick quartz window. A photomultipler tube, highly sensitive and very low-noise, detected light, which was converted into 9-bit digital video.
The digital video from each of two cameras was sent to the flyby spacecraft on a meter band channel at a data rate of 3072 bits/sec. This was then relayed to the Earth via a large parabolic antenna. In a typical style of redundant design, two entirely different radio systems were used for the interplanetary transmission. On a decimeter band, the digital video was passed unchanged, as a pulse-code modulated (PCM) signal. That is, pixel values were sent as a sequence of binary numbers (with convolution error-correction code). This is also how American spacecraft transmitted data.
On a centimeter band, an older Soviet radio system sent the data using a pulse magnetron to encode the data as variable spacing between powerful microwave impulses. 512 numbers per second were transmitted, each representing 6 bits of data and parity, encoded orthogonally into 128 possible pulse spacings. This scheme is usually called Pulse-position modulation (PPM), and in Russian VIM (Vremya Impulsnoi Modulyatsii).
Here are examples of two versions of transmitted video signal. The first is sent by PCM, generally a very clear signal, but single-bit errors create a familiar "salt & pepper" noise which gets more intense later in the transmission as the signal from the flyby spacecraft apparently weakens. The second image is sent by PPM and is rather strange. The noise takes the form of light speckles, but there is no sign of errors in low order bits. Even near the end of transmission, the noise characteristics remain unchanged. My own analysis found that I could systematically undo most of this noise, making these bad looking images actually a useful source of good data.
One of the objects Dr. Ksanfomality claims might be a lifeform is the "scorpion", which is indicated by the orange arrow. But his object does not appear in the simultaneously transmitted PCM signal.
To better understand this phenomenon, let us plot the corresponding pixel values in PCM and PPM versions (with log intensity). Along the diagonal, we see the hoped-for case where both pixels have the same value. The horizontal smear around this diagonal is the result of the "salt & pepper" noise contained in the PCM signal. However, the noise in the PPM signal is far from random, resulting in a geometrically patterned constellation of points. We would expect errors in pulse-position modulation to take the form of small errors in the pulse spacing, creating low-order bit errors. But these are passed through an orthogonal code that is designed to separate those values and make error correction easier. It is quite possible that the geometrical pattern is the result of that coding.
Noise in the PPM images tends to occur along isophotes, curves of constant brightness. And this explains why it follows subtle countours and develops into interesting structures. The "scorpion" and "disk" are probably the result of this phenomenon. However, Dr. Ksanfomality also points out a third unusual feature that changes over time, a dark shape next to the Prop-V sensor, a scientific experiment that drilled into the surface to measure the physical consistency of the rock.
Here are my own processed versions of two images taken about 15 minutes apart, which show a change in the shadow on the near side of the drill (under the smaller disk at the end of the framework). In my own research, I calculated a new and more accurate camera response function, so it is fairly clear that a shadow appears in the early image and then seems to be gone in the second image. But in the Russian versions of this image, the shadow is almost black, and this appears to be the object Dr. Ksanfomality named the "black rag".
While this is not an object that moved, it is still an interesting question to ask why the shadow disappeared. The illumination on the surface of Venus is thought to be a uniform glow from the perminantly cloudy sky. However, a few years ago, Grieger and Ignatiev analyzed spectral data from the Venera-13 lander, made during its descent, and they found evidence of a near-surface cloud layer. Could a passing low-altitude cloud have caused a change in the distribution of illumination?
I hope this controversy will kindle a rewnewed interest in the mysteries of the planet Venus and lead to new missions. The Soviet Union landed on Venus 10 times, and nobody has attempted it again since the twin landers of the 1985 Vega mission.