Tag Archives: mariner 2

[January 15, 1963] Venus’ true face (Scientific Results of Mariner 2)

[if you’re new to the Journey, read this to see what we’re all about!]


by Gideon Marcus

Remember five years ago, when Explorer 1 was launched?  At first, the big news was that America had answered Sputnik and joined the Space Age, but it soon became clear that the flight had larger significance.  For Explorer discovered the giant bands of hellish radiation that girdled the Earth, particles trapped by the Earth’s magnetic field.  Until 1957, these “Van Allen Belts” had been virtually unsuspected.  With one flight, our conception of the universe had drastically changed.

It’s happened again.

Mariner 2 is humanity’s first successful mission to another planet, and the scientific harvest is absolutely enormous.  Moreover, thanks to recent changes in policy, the initial results of this harvest were released unprecedentedly quickly (scientists are now reporting upon submission and acceptance of papers rather than publication).  Just one month since the probe’s encounter with Venus, the flood of information has been almost too much to parse; nevertheless, I think I’ve gotten the broad strokes:

Getting there is half the fun

Before I talk about Mariner’s encounter with Venus, it’s important to discuss what the spacecraft discovered on the way there.  After all, it was a 185 million mile trip, most of it in interplanetary space charted but once before by Pioneer 5.  And boy, did Mariner learn a lot!

For instance, it has finally been confirmed that the sun does blow a steady stream of charged particles in a gale known as the “Solar Wind.”  The particles get trapped in Earth’s magnetic field and cause, among other things, our beautiful aurorae. 

Mariner also measured the interplanetary magnetic field, which is really the sun’s magnetic field.  It varies with the 27-day solar rotation, and if we had more data, I suspect the overall map of the field would look like a spiral. 

Why is all this important?  Well, aside from giving us an idea of the kind of “space weather” future probes and astronauts will have to deal with, these observations of the sun’s effect on space give us a window as to what’s going on inside the sun to generate these effects. 

One last bit: along the way, Mariner measured the density of “cosmic dust,” little physical particles in space.  It appears that there’s a lot of it around the Earth, perhaps trapped by our magnetic field, and not a lot in space.  It may be that the solar wind sweeps the realm between the planets clean.

Unattractive planet

Given how magnetically busy the Earth is, and since Jupiter fairly crackles on the radio band thanks to its (likely) magnetic dynamo, one would expect Venus to impact its local space environment.  Nope.  In fact, Mariner 2 flew past the second planet without detecting a trace of Venusian magnetic field, nor any concentration of space dust around the planet.  Now, it’s possible that Venus has a weak field, or that its field is so oddly shaped that Mariner just hit a low patch, but the simplest explanation is usually the right one — Venus has no magnetic field.

Taking her temperature

Right up until December 14, some scientists (and many writers!) had held out hope that the thick clouds of Venus hid a reasonably hospitable surface, potentially teeming with life.  Earth-based sensors had indicated that the Venus was unbearably hot, but such could be explained by an unusually active Venusian ionosophere.  But as Mariner 2 turned its microwave and infrared radiometers across the face of Venus, it was clear that the edges of the planet were cooler than the center.  This is what one would expect from a hot surface, cooler atmosphere; the reverse would be expected of the “hot ionosphere” model.

So how hot is Venus?  At least 400 degrees Kelvin (260 degrees Fahrenheit), and probably a lot more.  There’s no way there is any liquid water under that hellish greenhouse of carbon dioxide.  Moreover, it’s not any nicer at night time.  There appears to be no real difference in temperature between the illuminated and dark halves of Venus, probably for the same reason the Earth’s oceans run a fairly consistent temperature – Venus’ atmosphere is thick enough for efficient distribution of warmth. 

Amtor dispelled

Mariner 2 and terrestrial radar have determined that the Venusian day incredibly long (~250 days, backward with respect to the other planets), but the Venusian winds blow across the planet far faster than the planet rotates; clouds have been seen racing around the disk of Venus in just 4-5 days.  Recent radar observations indicate that Venus’s surface is smoother than that of the Earth or the Moon. 

This, then, is our new picture of Venus.  It is a truly hellish place, more worthy of its less common moniker, Luciferos — a bleak, half-lit world scoured by hurricane-strength sandstorms hot enough to melt lead.  Bradbury’s All Summer in a Day, not to mention Burroughs’ “Venus” series’, will need some serious revision. 

Details, details

One of the nice things about sending a probe far from Earth is it allows for more accurate measurement of basic units – like the distance of the Earth and Venus from the sun.  This will help in future expeditions, manned and unmanned.  Another bit of bounty from Mariner’s flight is a refinement of the mass of Venus.  It is 81.485% that of Earth – one of the few ways Venus remains “Earth’s Twin.”

What’s next?

Opportunities to explore Venus occur every 19 months, when the second and third planets of the solar system are aligned in their orbits for easy travel.  Mariner 2 was so successful in its mission that NASA has canceled plans for a repeat flight in 1964.  Rather, the space agency will focus on Mars that year and follow up with Venus later, perhaps 1965. 

One reason to launch a new probe to Venus sooner rather than later is, despite the wealth of information passed back by Mariner 2, we did not get a single photograph of the planet.  That’s because the spacecraft was too small to carry the transmitting equipment required to send back pictures from so far away.  But by ’65, the new Centaur booster stage will have replaced the weaker Agena, which will allow a beefier payload. 

In the meantime, telemetry is worth a thousand pictures.  For now, let us revel in this scientific bonanza. Venus may not be a great place to live, but visiting has paid off tremendously.


(that’s rolls of data, not paper towels)

[P.S. If you registered for WorldCon this year, please consider nominating Galactic Journey for the “Best Fanzine” Hugo.  Check your mail for instructions…]




[December 14, 1962] Hot Stuff (Stop Press report on Mariner 2)

[if you’re new to the Journey, read this to see what we’re all about!]


by Gideon Marcus

The Space Race has given us a lot of firsts to report on in the last five years.  Today marks perhaps the most significant: for the first time, a spacecraft is reporting back to Earth on another world.  Mariner 2, launched on August 27, has traveled 182 million miles to fly by the second planet out from the sun, Venus.

It has been a perilous trip the entire way — even before the spacecraft ever left the ground!  Firstly, the mission almost didn’t leave the drawing board.  The original Mariner probe was a robust and heavy craft with a huge panoply of experiments.  But the beefy Atlas-Centaur booster wasn’t going to be ready in time for the next favorable orbital alignment of Earth and Venus, such occurring every 19 months.  Unless NASA wanted to wait until 1964…and risk being beat by the Russians, an alternative had to be found.

Luckily, the Ranger series of moon probes, half the size of the original Mariner and designed to fit on the smaller Atlas-Agena, was available.  Two new Rangers were adapted into “Mariner Rs” posthaste to meet the Summer 1962 deadline.  By July, Mariner 1 was on the launchpad.  This is where the second hurdle was met.

On July 22, Mariner 1’s Atlas soared into the sky.  93 seconds into the flight, the guidance antenna on board the rocket stopped hearing commands from ground control.  This was not immediately fatal; after all, the Atlas has its own computer with a program designed to keep the booster on course even without external direction.  Unfortunately, something was wrong with the program, too — probably a misprogrammed equation led the Atlas to make increasingly jerky maneuvers on its yaw axis.  Five minutes into the mission, ground control had to send a destruct order, blowing the rocket up in midflight.

A tense month went by.  Would the Russians beat us to the punch?  We’d gotten a reprieve the year before, when the Soviet probe Venera 1 sailed silently past the Planet of Love, its systems having died in flight.  On August 25, there were reports of a Soviet launch but no subsequent announcement of a new Venus mission.  Was it just a false alarm?  Or had our adversaries had troubles of their own?

Then Mariner 2 successfully launched, on August 27.  It made it through a mid-course correction on September 4 that put it on a course with destiny.  Now it just had to survive the journey, longer than any that had been managed before.  Given the track record of the Rangers (0 for 5), the odds weren’t good.

In fact, Mariner almost didn’t make it.  On Halloween, one of Mariner’s solar panels shorted out.  It came back on a week later only to short out for good on November 15.  Still, the crippled ship soldiered on closer to the sun, its remaining panel absorbing sufficient energy to power all instruments.  Mariner 2 set a record en route, continuing to send data past the point that Pioneer 5’s transmission faded away two years ago.  As the craft approached Venus, the temperature inside was close to boiling.

Nevertheless, little Mariner pulled through!  Passing just over 20,000 miles over the surface of Venus, Mariner 2 is sending back information, all experiments functioning.  As we speak, JPL engineers are poring through the data.  In just a few short weeks, we will finally have answers to some big questions: Is Venus really a roiling inferno?  How long is a Venusian day?  What is the nature of Venus’ magnetic field? 

Humanity has waited 100,000 years to learn the answers.  By January, we should have them.




[August 27, 1962] Bound for Lucifer (the flight of Mariner 2)

[if you’re new to the Journey, read this to see what we’re all about!]


by Gideon Marcus

If familiarity breeds contempt, then enigma must breed fascination.  So it has been with the planet Venus.  “Earth’s twin” in size and density, the second planet out from the sun is, in fact, the closest planet to us.  Yet, thanks to its shroud of clouds, very little can be determined of its nature.  At least, such was the state when I wrote my first article on the planet just three years ago.

Things are changing.

Opened eyes improve vision of Venus

Until recently, humanity was limited to examining the universe in the narrow band of light frequencies discernible to the eye.  That’s actually a tiny portion of the electromagnetic (EM) spectrum, which ranges from super-high frequency gamma rays, down through X-Rays, microwaves, and ultraviolet light, passes quickly through the visual light spectrum, and then to the lower-frequency infrared and radio waves.

In the last decade, we have developed ways of probing many of these EM bands from the Earth’s surface, and they have begun to reveal Venus’ true nature.  For instance, measuring microwave emissions from the planet, we find that the dark side simmers at a whopping 650 degrees Kelvin (710 degrees Fahrenheit).  Radio wave measurements seem to confirm this figure. 

The atmospheric pressure at “sea level” is some 50 times greater than on Earth.  It is not certain what components make up the Venusian atmosphere, but likely gases are Carbon Dioxide, Nitrogen, and water, in order of amount.  This combination is what causes the planet to swelter so – the air creates a greenhouse effect, trapping heat like a blanket.  The surface of Venus is probably like an oven, extremely dry (despite the potential for water vapor in high clouds), dimly lit by a blurry yellow sun, largely windless, and extremely inhospitable.  So much for the jungle-covered Amtor of Edgar Rice Burroughs.

Using radar, scientists have learned that Venus is more reflective than the moon (presumably the surface, or whatever the waves are bouncing off of, is smoother).  It has also been determined that Venus, if it rotates at all, does so extremely slowly.  A Venusian day may well be as long as its year: 225 days.  Scientists have used radar observations to confirm the greenhouse atmospheric model over others that had been advanced in the absence of data.  Radar also has given us a better idea exactly how far away the planet is from us, a critical piece of information for plotting the course of investigating spacecraft.  Which brings us to…

Let the onslaught begin

Every 19 months, the Earth and Venus are as favorably aligned in their orbits as they can get; that is the opportunity to send the heaviest spacecraft (i.e. with the most experiments) to investigate.  The first chance of the Space Age to send a probe to Venus took place in summer of 1959 – too soon for either superpower to loft a probe.  The United States did send up Pioneer 5 to the orbit of Venus in March 1960 to test long distance communications, however. 

The next alignment took place in February 1961.  No American probe was ready, but the Soviet http://galacticjourney.org/tag/venera-1/Venera 1 almost made it to Venus before mysteriously going silent. 

19 months have elapsed again, and this time, both major participants in the Space Race are ready.  Just a few days ago, the Soviets launched another Venera.  It failed to depart Earth’s orbit and will likely decay in a few days, but I can’t imagine it will be their only attempt.  Last month, America’s first try, Mariner 1, veered off course and had to be destroyed after only five minutes in flight.

Of course, I wouldn’t be talking about this if I didn’t have good news.  This morning, a new Mariner rose to the heavens atop an Atlas Agena rocket, and this one is safely on a course for the Planet of Love.

It’s a little probe, really a close cousin to the Ranger probes that have had such ill luck with the moon.  NASA had hoped to send a larger spacecraft, but the new Centaur second stage booster isn’t ready yet.  So the Agena-propelled Mariner carries just 40 pounds of equipment.  There’s no camera onboard, for Mariner lacks the cargo to carry a strong enough transmitter to send pictures. 

But there are several experiments that will be just as valuable.  For instance, there is a pair of radiometers that will tell us, once and for all, just how warm Venus really is.  There are a series of particle counters that will measure radiation both on the way to and in the vicinity of the planet.  This kind of exploration of interplanetary space has only been done once before, and it tells us volumes about the sun and how it affects us.  We will also learn about the fields of electrical force surrounding Venus.

To that end, Mariner 2 also carries a magnetometer, designed to tell us the strength and disposition of Venus’ magnetic field.  I’ve got a personal stake in this little experiment as two good friends, Chuck Sonett and Paul Coleman, are vital members of the team that built it.  These fine fellows worked in the private sector on Pioneer 5, and now NASA has seduced them onto the government payroll.  A win for the United States, I’d say!

So stay tuned.  Mariner will reach Venus in December, and if the probe still be active come then, you can bet there will be a bonanza of scientific results – and you’ll be able to read all about it at Galactic Journey!