Happy March Equinox: An Explanation

March Equinox graphic

Solstice and equinox diagram, showing the March equinox

Image Credit: NASA

Today is the March Equinox. You’ve probably already heard it a few times today; people running around proclaiming with utmost exuberance how today is the first day of Spring. After the long winters that some of us endure, the arrival of Spring is welcome news. But what is really going on today? After all, where I live it still feels like the middle of Winter, but flowers were already blooming on a trip I took to California a couple of weeks ago1. If we based “The First Day of Spring” on climate patterns, regions across the globe would be recognizing a wide variety of days throughout the year.

When someone says today is the first day of Spring, what they really mean (whether they know it or not) is that today represents an equinox; specifically, the March Equinox.2 On Earth, an equinox is the point in its orbit around the Sun when both hemispheres are equally illuminated; our tilted Earth lines up to a point in which the Sun passes directly over the equator. This happens twice a year, on the March and September equinoctes (which I learned today is the proper plural form of the word equinox).

Contrary to popular belief, the day of the equinox does not represent the day where daylight and darkness are equal. You can thank geometry, the atmosphere, and the Sun’s angular diameter to cause that equality to happen at different times geographically. What today does mean though, is that the equinoctes are the only two days in which the Sun rises due-East and sets due-West, and which the Sun would pass directly overhead from an observer on the equator.

One other very important thing that you must know if you don’t learn anything else today. Way too many people believe that the equinoctes are the only day of the year that an egg can be balanced on its end. While its true that on the equinox an egg can be balanced, it’s also true of every other day of the year; it makes no difference!

There are other times during the year (read: our orbit around the Sun) that we recognize Earth residing at a special place.  There’s Perihelion (which we went over in January) and Aphelion, and then the widely-celebrated solstices; but I’ll save that for another time.

Happy March Equinox!

This article originally posted on March 20, 2012.

  1. In fact, while it may have still been Winter to the San Diegans giving me quizzical looks for swimming in the ocean without a wet suit, to an Alaskan like myself it felt like an unusually warm Summer’s day!
  2. What about them being called the Spring  and Fall (or their Latin names, Vernal and Autumnal) equinoctes? Well, that wasn’t exactly fair to those in the Southern Hemisphere, whose seasons are opposite those in the Northern Hemisphere.

Juno: NASA’s Second New Frontiers Mission

Juno Mission Insignia

Juno Mission Insignia – Credit: NASA

NASA’s New Frontiers program is a set of solar system exploration missions designed to address “strategic goals in planetary science through a series of moderate size space missions” (you can read the entire program plan here). New Frontiers consolidates a number of long-term space missions into a single program that share a funding source, management structure, and goals, yet maintain their independent identities. New Horizons, NASA’s recent mission to Pluto and the Kuiper Belt, is considered the first mission of the New Frontiers program. The second mission is named Juno. Launched in 2011 with its sights set on our solar system’s red-spotted giant, Juno is poised to arrive at Jupiter on July 4, 2016. Let’s take a look at the mission and what we can expect to learn.

Juno: What’s In a Name?

Juno takes its name from Greek and Roman mythology. NASA draws the connection between the spacecraft and the myths as such:

Jupiter drew a veil of clouds around himself to hide his mischief. It was Jupiter’s wife, the goddess Juno, who was able to peer through the clouds and reveal Jupiter’s true nature. The Juno spacecraft will also look beneath the clouds to see what the planet is up to, not seeking signs of misbehavior, but helping us to understand the planet’s structure and history.


(It’s probably for the best that they left out the part about how Juno was, in addition to being Jupiter’s wife, also his sister.)

Juno Lifts Off

Juno Lifts Off – Credit: NASA/Bill Ingalls

Launch and Earth Fly-by

Juno launched atop the reliable and powerful Atlas V rocket engine on August 5, 2011. This engine contained five solid rocket boosters, along with a Centaur upper stage engine. The launch was flawless. After the solid rocket boosters were expended and jettisoned, the Centaur upper stage ignited and burned for six minutes, placing Juno in a parking orbit around the Earth. Juno coasted for thirty minutes towards the destination for the second Centaur burn. 40 minutes after lift-off from Cape Canaveral, the second Centaur burn was executed. It burned for nine minutes as it accelerated Juno on a trajectory to escape Earth’s orbit. From there, the Centaur engine separated from the spacecraft and Juno was on its own. Juno unfurled her solar panels and settled into a five-year journey to her mythical partner.

Juno underwent a series of deep space maneuvers that brought it back near Earth, two years and two months into its voyage. By now, Juno had already traveled 1.6 billion kilometers (994 million miles). Juno came within 559 kilometers (347 miles) of Earth, borrowing our planet’s gravity to boost its speed with an additional 3.9 kilometers per second (8,800 miles per hour). By the time Juno reaches Jupiter, it will have traveled more than 2,800 million kilometers (1.7 billion miles).

While near Earth, Juno did more than just steal some of our velocity. Juno’s science team activated a number of the spacecraft’s instruments and pointed them at Earth, acting as a sort of dress rehearsal for Jupiter.

Juno will be the second spacecraft to orbit and study Jupiter, preceded by the Galileo mission that performed from 1989 to 2003.

At Jupiter

Artist's concept art of Juno at Jupiter

Artist’s concept art of Juno at Jupiter – Credit: NASA/JPL-Caltech

Once Juno arrives at Jupiter on July 4, 2016, it will begin conducting its primary mission objectives. Juno will orbit Jupiter in a highly-elliptical orbit that will take it sweeping in close to the planet over one of its poles, zipping past the other pole in about two hours, before heading out beyond the orbit of Jupiter’s moon Callisto, repeating every 14 days.

Juno is loaded with instruments that will measure the oxygen and hydrogen ratios in Jupiter’s atmosphere, determine the mass of Jupiter’s core, map the gas giant’s magnetic and gravitational fields, and other important observations and experiments. These will allow us to determine how Jupiter formed, determine its structure below the clouds, and establish the source of the planet’s magnetic field.


Juno is also equipped with a visible light camera named JunoCam. Due to Jupiter’s damaging radiation and magnetic fields, JunoCam is only expected to operate for about 7 or 8 orbits; however, while it’s alive it’s expected to produce some fantastic images. Its specific targets will include Jupiter’s polar region and lower-latitude cloud belts, and will boast a resolution of 15 kilometers (9.3 miles) per pixel.

One of the best things about JunoCam is its strong emphasis on education and public outreach. For months now, a JunoCam website has been accepting images of Jupiter captured by amateur astronomers. These images will be publicly discussed during the next couple of months before a round of voting occurs to select the locations on Jupiter for JunoCam to image. Once the images have been captured and sent to Earth, the raw data will be posted on the JunoCam website for anyone to process and share.

Stay Tuned

If you want to stay up-to-date with the mission, you can watch the program page or follow the Twitter account below:

While you’re at it, you should follow the 46BLYZ Twitter account as well! Stay informed on Juno, and everything else space related.

ExoMars: Meet ESA’s Next Robotic Mars Explorer

Artist's impression depicting the separation of the ExoMars 2016 entry, descent and landing demonstrator module, named Schiaparelli, from the Trace Gas Orbiter, and heading for Mars.

Artist’s impression depicting the separation of the ExoMars 2016 entry, descent and landing demonstrator module, named Schiaparelli, from the Trace Gas Orbiter, and heading for Mars. – Source: ESA/ATG medialab

On Monday, March 14, 2016, the European Space Agency’s (ESA) robotic explorer, ExoMars, is slated to launch from the Baikonur Cosmodrome in Kazakhstan. Seven months later, ExoMars will arrive at the red planet and begin a number of scientific investigations that were designed to help determine whether live ever existed on Mars.

ExoMars Programme

ESA is establishing ExoMars as a two-part program (they spell it programme). The first is the part that’s launching in a few days: an orbiter with an entry, descent, and landing module. The second component is scheduled for a 2018 launch and will include a rover. Roscosmos, the Russian space agency, is a partner with the ESA for the entire program.

The goal of the program is to “demonstrate a number of essential flight and in-situ enabling technologies that are necessary for future exploration missions, such as an international Mars Sample Return mission” and to operate “a number of important scientific investigations”. The latter investigations are designed to search for both past and present life on Mars, understand how the water and geochemical environment varies across the planet, and sample Mars’s atmosphere.

This year’s mission includes an orbiter that will sample trace gases, as well as a landing module that study the environment at its landing site (it will be stationary once it lands). The lander even has a name: Schiaparelli. The name comes from the 17th century Italian astronomer Giovanni Virginio Schiaparelli.

Part of the entire program are a number of assessment tools to evaluate the performance of the various components of the mission, to aid in the design of future missions.

The planned 2018 mission will include a rover with a two-meter drill that will allow access deeper into the Martian soil than we have been able to get to before.

ExoMars 2016 in the Proton-M launcher at the launch pad in Baikonur, Kazakhstan.

ExoMars 2016 in the Proton-M launcher at the launch pad in Baikonur, Kazakhstan.
Credit: ESA – B. Bethge

You can watch a livestream of the video from this page: Watch ExoMars Launch. Coverage begins at 08:30 GMT (04:30 am Eastern Daylight Time) on March 14, with launch scheduled at 09:31 GMT (05:30 am Eastern Daylight Time).

You can also get updates on the mission from the ESA_ExoMars Twitter feed:

Arrival at Mars is expected on October 19, 2016. For more information on the mission, check out ESA’s mission site.

Looking Back on America’s First Female Astronauts

NASA Astronaut Group 8 class logo

NASA Astronaut Group 8 class logo – Credit: NASA

On January 16, 1978, NASA selected its first group of new astronauts since 1969. This new class of 35 astronaut candidates was named Astronaut Group 8, but colloquially referred to as the “TFNG: 35 New Guys”1 While there were 35 members of the class, for the first time they couldn’t all be referred to as “guys”. Astronaut Group 8 would produce many firsts in the way of diversity: the first African-American in space, the first Asian-American in space, and the first Jewish-American, among others. Today we highlight the six women of Astronaut Group 8: Shannon W. Lucid, Margaret Rhea Seddon, Kathryn D. Sullivan, Judith A. Resnik, Anna L. Fisher and Sally K. Ride. These would become America’s first female space explorers.

From left to right are Shannon W. Lucid, Margaret Rhea Seddon, Kathryn D. Sullivan, Judith A. Resnik, Anna L. Fisher, and Sally K. Ride. NASA selected all six women as their first female astronaut candidates in January 1978, allowing them to enroll in a training program that they completed in August 1979.

From left to right are Shannon W. Lucid, Margaret Rhea Seddon, Kathryn D. Sullivan, Judith A. Resnik, Anna L. Fisher, and Sally K. Ride. NASA selected all six women as their first female astronaut candidates in January 1978, allowing them to enroll in a training program that they completed in August 1979. – Credit: NASA

Shannon W. Lucid

Shannon Lucid in 1978

Shannon Lucid in 1978 – Source: NASA

Out of the six women of Astronaut Group 8, Shannon Lucid spent more time in space and flew on the most spaceflights. By the time she retired from NASA, she had flown to space on five separate flights and held a number of NASA spaceflight records as a result of her prolonged stay on the now-extinct Russian space station, Mir; Lucid was the only American woman that had the honor of serving upon Mir. In 1996, she became the first woman to receive a Congressional Space Medal of Honor which are awarded to astronauts “who in the performance of his duties has distinguished himself by exceptionally meritorious efforts and contributions to the welfare of the Nation and of mankind”. (Uhh, “his” and “himself”? Ahem!)  Of the six women in her class, Lucid was the only mother at the time of selection into the astronaut program (though, she wasn’t the first mother in space… we’ll get to that in a minute).

Lucid spent a total of 223 days, 2 hours, and  50 minutes in space during her career.

After her tenure as an astronaut, Lucid served as NASA’s Chief Scientist from February 2002 until September 2003. She also served as CAPCOM during numerous Space Shuttle and International Space Station crews. She retired from NASA in 2012.

Margaret Rhea Seddon

Margaret Rhea Seddon in 1978

Margaret Rhea Seddon in 1978 – Source: NASA

Margaret Rhea Seddon was the first medical doctor to travel to space. During her years as an astronaut, she flew on three separate missions. Her medical expertise was invaluable for the numerous experiments that she worked on during her missions in space, as well as the research she conducted on Earth. In 1981, Seddon married fellow Group 8 astronaut Robert L. Gibson and the two became the first active duty married astronauts.

During her three space flights, Seddon spent a total of 30 days, 2 hours, and 21 minutes in space. Her responsibilities during her 19 years at NASA included: helicopter search and rescue physician, serving on the NASA Life Sciences Advisory Committee and the NASA and International Bioethics Task Forces, and in-flight medical operations. While an active-duty astronaut, she continued to work part-time as an emergency room physician in various hospitals.

Seddon retired from NASA in 1997, remaining active in the medical community.

Kathryn D. Sullivan

Kathryn D. Sullivan

Kathryn D. Sullivan in 1990 – Source: NASA

Kathryn D. Sullivan made history in 1984 when she became the first American woman to conduct an EVA (extravehicular activity), spacewalking for 3-1/2 hours to demonstrate the feasibility of satellite refueling. This accomplishment came on her very first trip into space, during STS-41-G. In total, Sullivan visited space during three missions: STS-41-G, STS-31, and STS-45. STS-31 was an especially important mission, as they carried the Hubble Space Telescope into orbit, deploying it at an orbit altitude record at the time, of 612 kilometers (380 miles). Her work on STS-45, her final space voyage, included a number of research experiments as part of the Spacelab mission dedicated to the NASA ‘Mission to Planet Earth’. The results of that research provided a wealth of information about Earth’s climate and atmosphere.

During her three flights, she spent a total of 22 days, 4 hours, and 49 minutes in space.

In 2014, Sullivan was confirmed by the U.S. Senate to serve as the Under Secretary of Commerce for Oceans and Atmosphere and NOAA Administrator.

Anna L. Fisher

Anna Lee Fisher in 1980

Anna Lee Fisher in 1980 – Credit: John Bryson

In 1984, Anna Lee Fisher became the first mother in space. You might not immediately realize the significance of this, but I think it’s an important first. In the 1980s women were still fighting to be considered equals among men in the workplace. Much more so than now, moms were generally expected to stay home and raise the children while the fathers worked. So here you have a mother that not only does everything a mother does, but she works hard, trains to become an astronaut, and travels to space. Cracking the glass ceiling? More like smashing through Earth’s atmosphere!

Fisher is also extremely educated: she earned a Bachelor of Science in Chemistry in 1971, a Doctor of Medicine in 1976, and also earned a Master of Science in Chemistry in 1987–all from UCLA.

During her single flight, she spent 7 days, 23 hours, and 45 minutes in space.

As of 2014, Fisher was listed as a management astronaut with NASA and was working on NASA’s next generation crewed space program, among other duties.

(As an aside, the image of Anna Fisher above is one of my all-time favorite space images. The look of wonder and courage in her eyes stimulates some of the same emotions I had as a child watching these people take their trips into the skies in their shuttles. It represents a moment in our collective history, in which were just beginning to establish ourselves in a world that was much bigger than we had ever known before.)

Sally K. Ride

Sally Ride in 1984

Sally Ride in 1984 – Source: NASA

Sally Kristen Ride made history on June 18, 1983, when she became the first American woman in space (Russia put the first two women into space: Valentina Tereshkova and Svetlana Savitskaya). On that mission, STS-7, she also became the first woman to operate the shuttle’s robotic arm and the first to use it to retrieve a satellite from orbit. She flew a second flight in 1984, STS-41-G, with fellow Group 8 member Kathryn Sullivan.

During her two missions, she spent a total of 14 days, 7 hours, and 46 minutes in space.

In an interview with USA Today:

 In elementary school, there (were) lots of girls who were interested in science, and that’s true today. For whatever reason, I didn’t succumb to the stereotype that science wasn’t for girls. I got encouragement from my parents. I never ran into a teacher or a counselor who told me that science was for boys. A lot of my friends did.


Following the Challenger disaster, Ride served as a member of the Presidential Commission that investigated the accident. After NASA, Ride founded Sally Ride Science, a non-profit organization with a mission to “inspire young people in science, technology, engineering, and math (STEM) and to promote STEM literacy.”

Ride was always humble about it, but she was, and still is, a true inspiration to millions.

Ride passed away on July 23, 2012, while battling pancreatic cancer.

Judith A. Resnik

Judith Resnik in 1978

Judith Resnik in 1978 – Source: NASA

Not all of these stories have as happy of an ending as one would hope. On her second Shuttle mission, Judy Resnik was assigned to STS-51-L aboard Challenger. 73 seconds after lift-off, Challenger’s rocket boosters exploded and the orbiter broke apart. All seven members of the crew lost their lives.

Resnik earned a Bachelor of Science degree in Electrical Engineering from Carnegie-Mellon University in 1970, and a Doctorate in Electrical Engineering from University of Maryland in 1977.

Resnik’s first flight (STS-41-D), in 1984, made her the second American female in space, and the first Jewish-American in space. That mission had the crew deploy three satellites into orbit, as well as deploy the OAST-1 solar array. The array, once unfolded, was 13 feet wide and 102 feet long–“it’s up, and it’s big!” she reported to mission control. When folded, it was a mere 7 inches deep. The array demonstrated the feasibility of large lightweight solar arrays in space. Her total time in space as a result of that mission was 6 days, 56 minutes, and 4 seconds.

Resnik was posthumously awarded the Congressional Space Medal of Honor.

Judy Resnik aboard orbiter Discovery, during STS-41-D

Judy Resnik aboard orbiter Discovery, during STS-41-D – Source: NASA Spaceflight Forums


NASA's first female astronauts

NASA’s first female astronauts  – From left to right: Seddon, Sullivan, Resnik, Ride, Fisher, Lucid- Source: NASA

As of May 2015, nearly 60 women have flown into space. Along with Russian cosmonauts Valentina Tereshkova and Svetlana Savitskaya, these are the women that demolished barriers and showed the world that anyone that had the drive and work ethic required could make it in any industry that they desired to be a part of.

  1. Inside the space program, TFNG was a play on an off-color military phrase.

Galileo Spacecraft: First Orbiter of Jupiter

Artist rendering of Galileo arriving at Jupiter

Artist rendering of Galileo arriving at Jupiter – Credit: NASA

Space Shuttle Atlantis carried a special payload during its STS-34 mission. Commander Don Williams and crew transported the Galileo spacecraft into Earth orbit, from which point it was launched on a years-long voyage to Jupiter. Galileo would become the first spacecraft to orbit an outer planet and would go on to reveal fascinating views of the gas giant and its moons, as well as make monumental discoveries about the nature of the Jovian system.

Quick Facts:

  • Launch Date: October 18, 1989, Shuttle Atlantis STS-34
  • Primary Mission: October ’89 to December ’97.
  • Extended Missions: 3, from ’97 to ’03.
  • Number of Jupiter orbits: 34
  • Total distance traveled during mission: 4,631,778,000 km (approx 2.8 billion miles)
  • Mission End: September 21, 2003

Getting Galileo to Jupiter

Work on the Galileo craft began in 1977, after the exploration of Jupiter was listed as the number one priority in the Planetary Science Decadal Survey published in 1968. Fly-bys of the massive planet were conducted by the twin Pioneer 10 and 11 and Voyager 1 and 2 spacecrafts, but Galileo was set to do more than just perform a fly-by. It would launch an instrument-laden probe into Jupiter’s atmosphere, and then continue to orbit the planet for years. This mission would provide knowledge of the Jupiter system that could hardly even be imagined.

Galileo deploying from Shuttle Atlantis

Galileo deploying from Shuttle Atlantis – Credit: NASA

Galileo suffered a number of postponements. The first planned launch was to be from Space Shuttle Columbia in 1982, but development delays in the Space Shuttle program made that early of a launch unfeasible. The upside is that this gave the Galileo developers more time to work on the probe. Further planned launches and postponements occurred in 1984, 1985, and 1986.

As we all know, 1986 was the year of the Challenger disaster. Galileo would be put on hold during the 32-month hiatus that followed the tragedy, as every detail of the Shuttle program was examined and made safer. Galileo was originally planned to be attached to a liquid hydrogen-fueled Centaur-G booster; however, new safety protocols following Challenger prohibited the booster from being carried in the Space Shuttle’s payload bay. Mission designers had to reconsider how they would get Galileo from the Shuttle’s low Earth orbit to Jupiter. They decided on employing a solid-fuel Inertial Upper Stage booster (IUS). Whereas the Centaur-G would have propelled Galileo on a short and direct trajectory to Jupiter, the IUS would take longer and also require some technical gravitational slingshot maneuvers to make it to the gas giant.

Galileo was finally launched from Space Shuttle Atlantis, during mission STS-34 on October 18, 1989. From there, its IUS booster was started and it began its unique “VEEGA”, or Venus Earth Earth Gravity Assist, maneuvers.

Galileo spacecraft trajectory

Galileo spacecraft trajectory – Source: NASA

  • Galileo flew by Venus on February 10, 1990 at an altitude of 16,000 km (10,000 miles).
  • It then flew by Earth on December 8, 1990 at an altitude 960 km (597 miles).
  • Its trajectory took it near Asteroid Gaspra on October 29, 1991, coming within 1,601 km (1,000 miles).
  • Then it was back to another Earth fly-by on December 8, 1992, this time at an altitude of only 303 km (188 miles).
  • On its way back towards the outer solar system it flew by Asteroid Ida on August 28, 1993, coming within 2,400 km (1,400 miles) of the asteroid.

On its way to Jupiter, Galileo was positioned perfectly to observe the doomed Comet Shoemaker-Levy 9 as it impacted the planet. Pieces of the comet, having been torn into fragments by Jupiter’s immense tidal forces, impacted Jupiter from July 16 – 22, 1994, on the side facing away from Earth. Fortunately, Galileo had a prime view and was able to record the impact. Earth-based telescopes could only observe the impact sites as they rotated into view a few minutes afterwards.

In July, 1995, Galileo released its atmospheric probe component. For the next five months, the probe and orbiter continued their cruise to Jupiter. On December 7, 1995, Galileo had arrived. The orbiter and probe diverged onto their separate missions.

Atmospheric Probe

On December 7, 1995 Galileo’s atmospheric probe sliced into Jupiter’s atmosphere at 47.6 kilometers per second (106,000 miles per hour). As the atmosphere began to slow the probe, it deployed its drogue and main parachutes and dropped its heat shield to expose its scientific instruments. The probe began recording data and transmitting it up to the main Galileo spacecraft orbiting high above, which then re-transmitted the data to Earth. The probe recorded 58 minutes of data on Jupiter’s weather and atmosphere. Towards the end of its descent, the probe measured wind speeds of 724 kilometers per hour (450 miles per hour). The intense heat and pressure of Jupiter’s atmosphere melted and vaporized the probe less than an hour into its journey through Jupiter’s atmosphere.


While the atmospheric probe’s job was complete, the Galileo orbiter still had years of work left to do. The orbiter received its electric power from two radioisotope thermoelectric generators (RTGs). That may sound complicated, but it’s really quite simple. These RTGs carry the radioactive element plutonium-238. As the plutonium decays, it releases energy in the form of heat. That heat can then be easily turned into electricity through the Seebeck effect. This type of energy generation is long-lasting and reliable, as well as impervious to the cold temperatures and strong radiation fields of the Jupiter system. Galileo carried two of these RTGs, with a combined total of approximately 22.7 kilograms (50 pounds) of plutonium-238. While these radioactive components had been used on previous space missions, Galileo drew extra concern due to it being both carried by the Shuttle as well as the multiple Earth fly-bys. Anti-nuclear activists protested Galileo’s launch, fearing a malfunction could cause radiation poisoning for many thousands of people on Earth. NASA, however, argued that the probability of risk was extremely low.

Jupiter's ring system, as observed by Galileo

Jupiter’s ring system, as observed by Galileo – Credit: NASA/JPL/Cornell University

Galileo conducted slow orbits of Jupiter, approximately 2 months long each. The orbits were elongated, and designed to bring the spacecraft within different distances to Jupiter, which allowed it to sample different areas of the planet’s magnetosphere. These orbits were also designed to bring Galileo and its instruments into close fly-bys of Jupiter’s largest moons. Galileo completed its primary mission on December 7, 1997; however, the craft was still functioning extremely well and was able to continue taking measurements and sending valuable data back to Earth. Its mission was extended three times, operating until 2003.

Volcanic activity on Io, as observed by Galileo

Volcanic activity on Io, as observed by Galileo – Credit: NASA/JPL

The orbiter made several discoveries during its mission:

  • It discovered a possible ocean under Europa’s icy crust
  • Revealed Ganymede’s very own magnetic field, the only moon known to have this feature
  • Made the first observations of ammonia clouds in another planet’s atmosphere
  • It created hundreds of images of Jupiter’s large ‘Galilean moons’: Io, Callisto, Europa, and Ganymede
  • It measured the high levels of volcanic activity on Io

Sagan Criteria for Life

The late astronomer Carl Sagan devised a set of experiments to be conducted by Galileo during its first fly-by of Earth. The purpose of the experiments was to see if life could be easily detected from a spacecraft. The results of the experiments were published by Sagan in 1993, in the scientific journal Nature. The experiments were a success, as Galileo was easily able to detect what are referred to as the ‘Sagan requirements for life’. These include strong absorption of light at the red end of the spectrum (indicative of plant photosynthesis), absorption bands of molecular oxygen (again, indicative of plant life), the detection of methane in the atmosphere (a gas created by either volcanic or biological activity), and the detection of narrowband radio wave transmissions (could indicate a technologically advanced civilization).

By the end of its mission, Galileo had conducted 34 orbits of Jupiter and had made multiple fly-bys of Jupiter’s moons: Io 7 times, Callisto 8 times , Ganymede 8 times, Europa 11 times, and one fly-by of Amalthea.

Due in part to Galileo’s discovery of potential oceans on Europa (and possibly other Jovian moons), the decision was made to end the orbiter’s mission by sending it to the same fate as the atmospheric probe eight years prior. Rather than risk contaminating (with either Earth bacteria or radiation from the RTGs) one of Jupiter’s potentially life-harboring moons, Galileo would be ordered to impact Jupiter. On September 21, 2003, Galileo entered Jupiter’s atmosphere at 48.2 kilometers per second (108,000 mph).

The Galilean Moons: Jupiter's four largest satellites

The Galilean Moons: Jupiter’s four largest satellites – Credit: NASA/JPL/DLR

The total mission cost was approximately $1.4 billion USD, had more than 100 scientist partners from many different countries, and involved the work of more than 800 individuals.

In spite of postponements, an antenna that failed to fully deploy, and a tape recorder malfunction, Galileo performed magnificently. It was a mission that brought us up close and personal with our Solar system’s largest planet and provided us with a much more detailed understanding of the Jovian system. Galileo paved the way for future studies of Jupiter and its moons. Its successor, the Juno orbiter, is currently en route and arriving in July of 2016, and plans are being considered to investigate Europa’s oceans. Like the astronomer that the spacecraft took its name from, Galileo Galilei, this mission revealed new worlds that we previously could only distantly wonder about.