New Photos of Saturn and Mars from Hubble

During the summer of 2018, the planets of Mars and Saturn (one after the other) have been in opposition. In astronomical terms, opposition refers to when a planet is on the opposite side of the Earth relative to the Sun. This not only means that the planet is closer to Earth in its respective orbit, but that is also fully lit by the Sun (as seen from Earth) and much more visible.

As a result, astronomers are able to observe these planets in greater detail. The Hubble Space Telescope took advantage of this situation to do what it has done best for the past twenty-eight years – capture some breathtaking images of both planets! Hubble made its observations of Saturn in June and Mars in July, and showed both planets close to their opposition.

Hubble’s high-resolution images of the planets and moons in our Solar System can only be surpassed by spacecraft that are either orbiting or conducting close flybys to them. However, Hubble has a major advantage over these types of missions, in that it can look at the Solar planets periodically and observe them over much longer periods of time than a passing spacecraft.

This composite image, taken by the NASA/ESA Hubble Space Telescope on June 6th, 2018, shows the ringed planet Saturn with six of its 62 known moons. Credit: NASA, ESA, A. Simon (GSFC) and the OPAL Team, and J. DePasquale (STScI)

Hubble observed Saturn on June 6th, almost a month before it reached opposition on June 27th. At the time, the ringed gas giant was approximately 1.4 billion km (870 million mi) from Earth. Hubble was able to capture the planet’s magnificent ring system at a time when it was at its maximum tilt to Earth, which allowed for a spectacular view of the rings and the gaps between them.

Hubble’s new image of Saturn also managed to capture the hexagonal storm around the gas giant’s north pole. This stable and persistent jet stream was first observed by the Voyager 1 probe during its flyby of Saturn in 1981, and has been a mystery to astronomers ever since. On top of that, the new image also features six of Saturn’s 62 known moons – Dione, Enceladus, Tethys, Janus, Epimetheus, and Mimas.

Hubble’s new image of Mars was captured on July 18th, 13 days before it reached its closest approach to Earth. This year will see the Red Planet get as close as 57.6 million km from Earth, which is the closest approach made since 2003. On that occasion, Mars was just 55,757,930 km (34,647,420 mi) from Earth, which was the closest the planet had been to Earth in almost 60,000 years!

Mars is at opposition to Earth every two years, so Hubble has had many opportunities to capture detailed images of the planet’s surface. However, this new image is different in that it is dominated by a gigantic sandstorm that is currently encompassing the entire planet. This storm has been raging since May of 2018 and developed into a planet-wide dust storm within several weeks.

In mid-July the NASA/ESA Hubble Space Telescope observed Mars, only 13 days before the planet made its closest approach to Earth in 2018. Credit: NASA, ESA, and STScI

Dust storms are a common occurrence on Mars. They take place every year, usually stay contained to a local area, and normally last only about a few weeks. Larger dust storms that can grow to cover the entire planet are a rarer event, and can typically last for weeks or even months. These tend to happen during the spring and summer months in the southern hemisphere, which coincides with Mars being closer to the Sun in its elliptical orbit.

Due to increased temperatures, dust particles are lifted higher into the atmosphere, creating more wind. The resulting wind kicks up yet more dust, creating a feedback loop that NASA scientists are still trying to understand. While spacecraft orbiting Mars and rovers and lander can study storm behavior at lower altitudes or from the surface, Hubble observations allow astronomers to study changes in the higher atmosphere.

The combined observations will help planetary scientists to better understanding how these global storms arise. Despite the obscuring dust storm, Hubble still managed to capture several important Martian surface features like the polar ice caps, Terra Meridiani, the Schiaparelli Crater, and Hellas Basin – even though all of them appear slightly blurred in the image.

The Hellas Basin – an impact basin that measures 2200 km (1367 mi) across and is nearly 8 km (4.97 mi) deep – is visible at the lower right and appears as a large and bright oval area. The orange area in the upper center of the image is Arabia Terra, a large upland area in northern Mars. This region is characterized by many impact craters and heavy erosion, which indicates that it could be among the oldest terrains on the planet.

This annotated image of Mars shows features of the planet that were visible in summer 2018 despite a global dust storm. Credit: NASA, ESA, and STScI

South of Arabia Terra are the dark streaks known as Sinus Sabaeus and Sinus Meridiani, features that stretch from east to west along the equator and are made of up dark bedrock and sand deposits from ancient lava flows. Because it was autumn in the northern hemisphere when the image was taken, it is covered in a bright blanket of clouds – and clouds can also be seen above the northern and southern polar ice caps. Last, but not least, Mars’ two small moons – Phobos and Deimos – appear in the lower half of the image.

Comparing these new images of Mars and Saturn with older data gathered by Hubble, other telescopes and the many probes that have taken images of them over the years will allow astronomers to study how cloud patterns and large-scale structures on the Solar planets change over time. These latest images also show that even after almost three decades of being in operation, Hubble is still able to pull its weight!

And be sure to enjoy this video about the images acquired by Hubble, courtesy of Hubblecast:

Further Reading: Hubble

Summer Astronomy, Minimoon & Saturn Opposition 2017

Saturn on June 1st, nearing opposition. Image credit and copyright: Peter on the Universe Today Flickr forum

Summertime astronomy leaves observers with the perennial question: when to observe? Here in Florida, for example, true astronomical darkness does not occur until 10 PM; folks further north face an even more dire situation. In Alaska, the game in late July became “on what date can you first spot a bright planet/star? around midnight.

And evening summer thunder showers don’t help. Our solution is to get up early (4 AM or so) when the roiling atmosphere has settled down a bit.

But there’s one reason to stay up late, as the planet Saturn reaches opposition next week on June 15th and crosses into the evening sky.

Southern hemisphere observers have it best this year, as the ringed planet loiters in southern declinations for the next few years. In fact, Saturn won’t pop up over the celestial equator again until April, 2026. You’ll still be able to see Saturn from mid-northern latitudes, looking low to the south.

First, a brief rundown of the planets this summer. Mars is currently on the far side of the Sun and headed towards solar conjunction of July 26th. Meanwhile, Mercury is headed towards greatest eastern (dusk) elongation on June 21st. Early AM viewers, can follow Venus, which has just passed greatest elongation west of the Sun on June 3rd, just last week. Finally, Jupiter joins Saturn in the dusk sky, high to the south at sunset and headed towards quadrature 90 degrees east of the Sun on July 6th.

Looking eastward on the evening of June 9th. Credit: Stellarium.

There’s another astronomical curiosity afoot this coming weekend: the MiniMoon for 2017. This is the Full Moon nearest to lunar apogee, a sort of antithesis of the over-hyped “SuperMoon.” Lunar apogee occurs on Thursday, June 8th and the Full Moon occurs just 14 hours after.

2017 sees Saturn traveling from the dreaded “13th constellation” of zodiac Ophiuchus the Serpent Bearer into Sagittarius. This also means that Saturn is headed towards bottoming out near 23 degrees southern declination next year in late 2018. Saturn truly lives up to its “father time” namesake, marking up its slow 29 year passage once around the zodiac. This struck home to us a few years back when Saturn passed Spica in the constellation Virgo, right back where I first started observing the planet as a teenager three decades before.

The path of Saturn through the last half of 2017. Credit: Starry Night Education Software.

The rings are also at their widest tilt in 2017, making for an extra photogenic view. 27 degrees wide as seen from our Earthly vantage point is as wide as Saturn’s ring system ever gets. Saturn isn’t really “tipping” back and forth as much as it’s orbiting the Sun and dipping one hemisphere towards us, and then another. In 2017, it’s the planet’s northern hemisphere time to shine.

Saturn: the changing view. Image credit and copyright: Andrew Symes (@failedprotostar)

Here’s the last/next cycle rundown:

-Rings wide open: (southern pole of Saturn tipped earthward): 2003

Rings edge on: 2009

Rings wide open: (northern pole of Saturn tipped earthward): 2017

-Rings edge on: 2025

-Rings wide open: (southern pole of Saturn tipped earthward): 2032

Even a small 60 mm refractor and a low power eyepiece will reveal the most glorious facet of Saturn: its glorious rings. Galileo first saw this confounding view in 1610, and sketched Saturn as a curious double-handled world. In 1655 Christaan Huygens first correctly deduced that Saturn’s rings are a flat plane, fully disconnected from the planet itself.

Crank up the magnification a bit, and the large Cassini Gap in the rings and the shadow play of the rings and the planet becomes apparent. This gives the view an amazing 3-D effect unparalleled in observational astronomy. The shadow cast by the bulk of the planet disappears behind it during opposition, then slowly starts to reemerge to one side after. Other things to watch for include the retro-reflector Seeliger Effect ( also known as opposition surge) as the planet brightens near opposition. And can you spy the bulk of the planet through the Cassini gap?

The moons of Saturn. Image credit and copyright: John Chumack

Hunting for Saturn’s moons is also a fun challenge. Saturn has more moons visible to a backyard telescope than any other planet. Titan is easiest, as the +8 magnitude moon orbits Saturn once every 16 days. In a small to medium-sized (8-inch) telescope, six moons are readily visible: Enceladus, Mimas, Rhea, Dione, Iapetus and Tethys. Large light bucket scopes 10” and larger might just also tease out the two faint +15th magnitude moons Hyperion and Phoebe.

Saturn
Cassini looks back across Saturn’s rings. NASA/Cassini/JPL-Caltech/Space Science Institute

There’s also something else special about Saturn in 2017 in the world of space flight: the venerable Cassini mission comes to an end this September. Hard to believe, this mission soon won’t be with us. Launched in 1997, Cassini arrived at Saturn in in July 2004, and has since provided us with an amazing decade plus of science. The internet and science writing online has grown up with Cassini, and it’ll be a sad moment to see it go.

All thoughts to ponder, as you check out Saturn at the eyepiece this summer.

Mars At Closest Point To Earth in 11 Years May 30, 2016

Mars in all its red-hued glory. Image: NASA, ESA, the Hubble Heritage Team (STScI/AURA), J. Bell (ASU), and M. Wolff (Space Science Institute)

If you have a telescope, (What?! You don’t have one?) you’re in for a visual treat tonight. Mars will be at its closest point to Earth in 11 years on May 30. This event is worth checking out, whether with a telescope, astronomy binoculars, or online.

While today is when Mars is at its closest, you actually have a couple weeks to check this out, as the distance between Mars and Earth gradually becomes greater and greater. Today, Mars is 76 million kilometers (47.2 million miles) away, but up until June 12th it will still be no further than 77 million kilometers (48 million miles) away.

The furthest Mars can be from Earth is 401 million kilometers (249 million miles), when the two planets are on the opposite side of the Sun from each other.

For most of us with backyard ‘scopes, it’s difficult to make out much detail. You can see Mars, and at the most you can make out a polar cap. But it’s still fascinating knowing you’re looking at another planet, one that was totally unknowable for most humans who preceded us. A planet that we have rovers on, and that we have several craft in orbit around.

If you don’t have a scope, have no fear. There will be a flood of great astro-photos of Mars in the next few days. There are also options for live streaming feeds from powerful Earth-based telescopes.

The last time Mars was this close to Earth was 2005. A couple years before, the distance shrank to 55.7 million km (34.6 million miles.) That was the closest Mars and Earth have been in several thousand years. In 2018, the two planets will be nearly that close again.

This event is often called “opposition”, but it’s actually more correctly called “closest approach.” Opposition occurs a couple weeks before closest approach, when Mars is directly opposite the Sun.

A top-down image of the orbits of Earth and Mars. Image: NASA
A top-down image of the orbits of Earth and Mars. Image: NASA

But whether you call it opposition, or closest approach, the event itself is significant for more than just looking at it. Missions to Mars are planned when the two planets are close to each other. This reduces mission times drastically.

Mars Express, the mission being conducted by the European Space Agency (ESA) was launched in 2003, when the two planets were as close to each other as they’ve been in thousands of years. All missions to Mars can’t be so lucky, but they all strive to take advantage of the orbital cycles of the two planets, by nailing launch dates that work in our favour.

As for finding Mars in the night sky, it’s not that difficult. If you have clear skies where you are, Mars will appear as a bright, fire-yellow star.
“Just look southeast after the end of twilight, and you can’t miss it,” says Alan MacRobert, a senior editor of Sky & Telescope magazine, in a statement. “Mars looks almost scary now, compared to how it normally looks in the sky.”

This image shows how Mars appears at different times of the year in a typical backyard telescope. Image: NASA/JPL-Caltech
This image shows how Mars appears at different times of the year in a typical backyard telescope. Image: NASA/JPL-Caltech

Although Mars is the closest thing in the sky to Earth right now, other than the Moon, it isn’t the brightest thing in the night sky. That honour is reserved for Jupiter, even though it’s ten times further away. Jupiter is twenty times larger in diameter than Mars, so it reflects much more sunlight and appears much brighter. (Obviously, everything in the night sky pales in comparison to the Moon.)

The reason for such a variation in distances between the planets lies in their elliptical orbits around the Sun. There’s a great video showing how their orbits change the distance between the two planets, here.

If you don’t have a telescope, you can still check Mars out. Go to slooh.com to check out live feeds from a proper telescope.

Hubble Telescope Zooms In On Mars

This image shows our neighbouring planet Mars, as it was observed shortly before opposition in 2016 by the NASA/ESA Hubble Space Telescope. Some prominent features of the planet are clearly visible: the ancient and inactive shield volcano Syrtis Major; the bright and oval Hellas Planitia basin; the heavily eroded Arabia Terra in the centre of the image; the dark features of Sinus Sabaeous and Sinus Meridiani along the equator; and the small southern polar cap.
On May 12, the Hubble Space Telescope took this photo of Mars. Some prominent features of the planet are clearly visible: the ancient and inactive shield volcano Syrtis Major (far right and partly covered by clouds); the heavily eroded Arabia Terra in the center of the image; the dark features of Sinus Sabaeous and Sinus Meridiani below center and the small north polar cap (top).

We’re in store for an exciting weekend as the Earth and Mars get closer to each other than at any time in the last ten years. To take advantage of this special opportunity, the Hubble Space Telescope, normally busy eyeing remote galaxies, was pointed at our next door neighbor to capture this lovely close-up image.

Opposition occurs when Mars and Earth line up on the same side of the Sun. The two planets are closest together at that time. Mars opposition occurs on May 22, when the planet will shine at magnitude -2.0 and with an apparent diameter of 18.6 arc seconds, its largest in years. Credit: Bob King
Opposition occurs when Mars and Earth line up on the same side of the Sun. The two planets are closest together around that time. Mars opposition occurs on May 22, when the planet will shine at magnitude -2.0 and with an apparent diameter of 18.6 arc seconds, its largest in over 10 years. Credit: Bob King

As Universe Today writer David Dickinson described in his excellent Mars guide, the planet reaches opposition on Sunday morning May 22. That’s when the planet will be directly opposite the Sun in the sky and rise in the east around the same time the Sun sets in the west. Earth sits squarely in between. Opposition also marks the planet’s close approach to Earth, so that Mars appears bigger and brighter in the sky than usual. A perfect time for detailed studies whether through both amateur and professional telescopes.

Although opposition for most outer planets coincides with the date of closest approach, that’s not true in the case of Mars. If Mars is moving away from the Sun in its orbit when Earth laps it, closest approach occurs a few days before opposition.  But if the planet is moving toward the Sun when our planet passes by, closest approach occurs a few days after opposition. This time around, Mars is headed sunward, so the date of closest approach of the two planets occurs on May 30.

It’s all goes back to Mars’ more eccentric orbit, which causes even a few days worth of its orbital travels to make a difference in the distance between the two planets when Earth is nearby.  On May 22, Mars will be 47.4 million miles away vs. 46.77 million on the 30th, a difference of about 700,000 miles.

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Every 26 months Mars reaches opposition. This mosaic of photos taken by Hubble show seven different oppositions since 1995. Because of Mars’ elliptical orbit, it shows variations in apparent size from opposition to opposition.  Mars was the closest in 2003 when it came within 34.8 million miles (56 million kilometer) of Earth. The part of Mars that is tilted towards the Earth also shifts over time, resulting in the changing visibility of the polar caps. Clouds and dust storms, as well as the size of the ice caps, can change the appearance of Mars on time scales of days, weeks, and months. Other features of Mars, such as some of the large dark markings, have remained unchanged for centuries. Credit: NASA/ESA

On May 12, Hubble took advantage of this favorable alignment and turned its gaze towards Mars to take an image of our rusty-hued neighbor, From this distance the telescope could see Martian features as small as 18.6 miles (30 kilometers) across. The image shows a sharp, natural-color view of Mars and reveals several prominent geological features, from smaller mountains and erosion channels to immense canyons and volcanoes.

This image shows our neighbouring planet Mars, as it was observed shortly before opposition in 2016 by the NASA/ESA Hubble Space Telescope. Some prominent features on the surface of the planet have been annotated.
Some of the more prominent features in the Hubble photo of Mars are marked here. Limb hazes are visible in modest-sized telescopes as a pale edging around the planet’s rim. The planet’s distinctive red color is created by rust. Billions of years ago, it’s thought that ultraviolet light from the Sun split water in the Martian atmosphere into hydrogen and oxygen. The hydrogen escaped, but the oxygen combined with iron in the planet’s surface rocks to form iron oxide or rust. Many of Earth’s red rock formations are similarly “oxidized.” Credit: NASA/ESA

The orange area in the center of the image is Arabia Terra, a vast upland region. The landscape is densely cratered and heavily eroded, indicating that it could be among the oldest features on the planet.

While the polar caps aren't currently visible, telescope users will be treated to nice views of India-shaped Syrtis Major. The large crater Hellas at the top (south) limb is currently covered in winter clouds. Credit: Christopher Go
While the polar caps aren’t currently visible, telescope users will be treated to nice views of India-shaped Syrtis Major. The large crater Hellas at the top (south) limb is currently covered in winter clouds. Credit: Christopher Go

South of Arabia Terra, running east to west along the equator, is the long dark feature named Sinus Sabaeus that terminates in a larger, dark blob called and Sinus Meridiani. These darker regions are covered by bedrock from ancient lava flows and other volcanic features. An extended blanket of clouds can be seen over the southern polar cap where it’s late winter. The icy northern polar cap has receded to a comparatively small size because it’s now late summer in the northern hemisphere.

Mars on May 2 shows Syrtis Major off to the east (right). Crossing the top of the photo are Mare Tyrrhenum to the right of the planet's central meridian and Mare Cimmerium, to the left. Credit: Christopher Go
Mars on May 2 shows Syrtis Major off to the east (right). Crossing the top of the photo are Mare Tyrrhenum to the right of the planet’s central meridian and Mare Cimmerium, to the left. Credit: Christopher Go

So the question now is how much will you see as we pull up alongside the Red Planet this weekend? With the naked eye, Mars looks like a fiery “star” in the head of Scorpius the scorpion not far from the similarly-colored Antares, the brightest star in the constellation. It’s unmistakable. Even through the haze it caught my eye last night, rising in the southeast around 10 o’clock with its signature hue.

Through a 4-inch or larger telescope, you can see limb hazes/clouds and prominent dark features such as Syrtis Major, Utopia, clouds over Hellas, Mare Tyrrhenum (to the west of Syrtis Major) and Mare Cimmerium (west of M. Tyrrhenum).

Expert imager Damian Peach created this photographic map of Mars labeled with its most prominent features visible in amateur telescopes. Click for a larger version. Credit: Damian Peach
Expert astroimager Damian Peach created this photographic map of Mars labeled with its most prominent features visible in amateur telescopes. Click for a large version. Credit: Damian Peach

These features observers across the America will see this week and early next between about 11 p.m. and 2 a.m. local time. As Mars rotation period is 37 minutes longer than Earth’s, these markings will gradually rotate out of view, and we’ll see the opposite hemisphere in the coming weeks. You can use the map to help you identify particular features or Sky & Telescope’s handy Mars Profiler to know which side of the planet’s visible when.

The Full Moon, Mars only hours before opposition, Saturn and Antares gather in the southern sky for a special, diamond-shaped grouping. Diagram: Bob King, source: Stellarium
The Full Moon, Mars only hours before opposition, Saturn and Antares gather in the southern sky for a special, diamond-shaped grouping. Diagram: Bob King, source: Stellarium

To top off all the good stuff happening with Mars, the Full Flower Moon will join up with that planet, Saturn and Antares Saturday night May 21 to create what I like to call a “diamond of celestial lights” visible all night. Don’t miss it!

Italian astronomer Gianluca Masi will offer up two online Mars observing sessions in the coming week, on May 22 and 30, starting at 5 p.m. CDT (22:00 UT). Yet another opportunity to get acquainted with your inner Mars.

Jupiter and the Full Snow Moon Come Together In a Beautiful Conjunction Tonight

The Full Moon celebrates Jupiter’s coming opposition by accompanying the bright planet in a beautiful conjunction tonight.

Even last night Jupiter and the Moon were close enough to attract attention. Tonight they’ll be even more striking. Two reasons for that. The Moon is full this evening and will have crept within 41/2° of the planet. They’ll rise together and roll together all night long.

The Full Snow Moon will share the sky with Jupiter in Cancer tonight not far from the Sickle or head of Leo the Lion.  The map shows the scene around 8 o'clock local time. Source: Stellarium
The Full Snow Moon will share the sky with Jupiter in Cancer tonight not far from the Sickle or head of Leo the Lion. The map shows the scene around 8 o’clock local time. Source: Stellarium

February’s full moon is aptly named the Full Snow Moon as snowfall can be heavy this month. Just ask the folks in Chicago. The Cherokee Indians called it the “Bone Moon”, named for the tough times experienced by many Native Americans in mid-winter when food supplies ran low. With little left to eat people made use of everything including bones and bone marrow for soup.

Not only is the Full Moon directly opposite the Sun in the sky, rising around sunset and setting around sunrise, but in mid-winter they’re nearly on opposite ends of the celestial seesaw.

Jupiter, like tonight's Full Moon, will be directly opposite the Sun this Friday and in "full moon" phase. Credit: Bob King
Jupiter, like tonight’s Full Moon, will be directly opposite the Sun this Friday and in “full moon” phase. Because both planets are lined up on the same side of the Sun, Jupiter will also be at its closest to us for the year. Credit: Bob King

In early February the Sun is still near its lowest point in the sky (bottom of the seesaw) for the northern half of  the globe. And while daylight is steadily increasing as the Sun moves northward, darkness still has the upper hand this month. Full Moons like tonight’s lie 180° opposite the Sun, placing the Moon near the top of the seesaw. Come early August, the Sun will occupy the Moon’s spot and the Full Moon will have slid down to the Sun’s current position. Yin and Yang folks.

Now here’s the interesting thing. Jupiter will also be in “full moon” phase when it reaches opposition this Friday Feb. 6.  Take a look at the diagram. From our perspective on Earth, Jupiter and the Sun lie on opposite sides of our planet 180° apart. As the Sun sets Friday, Jupiter will rise in the east and remain visible all night until setting around sunrise exactly like a Full Moon.

So in a funny way, we have two Full Moons this week only one’s a planet.

Like me, a lot of you enjoy a good moonrise. That golden-orange globe, the crazy squished appearance at rising and the transition to the bright, white, beaming disk that throws enough light on a winter night to ski in the forest without a headlamp. All good reasons to be alive.

If Jupiter were moved to the Moon's distance it would span about 20 of sky or 40x the apparent diameter of the Full Moon. Credit: Roscosmos with additions by the author
If Jupiter were moved to the Moon’s distance it would span about 20 degrees or 40 times the apparent diameter of the Full Moon. Credit: Roscosmos with additions by the author

To find when the moon rises for your town, click over to this moonrise calculator. As you step outside tonight to get your required Moon and Jupiter-shine, consider the scene if we took neighboring Jupiter and placed it at the same distance as the Moon. A recent series of such scenes was released by the Russian Federal Space Agency (Roscosmos). I included one here and added the Moon for you to compare. Is Jupiter enormous or what?

How Far is Mars from Earth?

This article was originally published on Aug 10, 2012. We’ve updated it and added this cool new video!

Sending spacecraft to Mars is all about precision. It’s about blasting off from Earth with a controlled explosion, launching a robot into space in the direction of the Red Planet, navigating the intervening distance between our two planets, and landing with incredible precision.

This intricate and complicated maneuver means knowing the exact distance from Earth to Mars. Since Mars and Earth both orbit the Sun – but at different distance, with different eccentricities, and with different orbital velocities – the distance between then is constantly changing

The first person to ever calculate the distance to Mars was the astronomer Giovanni Cassini, famous for his observations of Saturn. Giovanni made observations of Mars in 1672 from Paris, while his colleague, Jean Richer made the same observation from Cayenne, French Guiana. They used the parallax method to calculate the distance to Mars with surprising accuracy.

About every two years, however, the Earth passes Mars as they orbit around the Sun. Credit: NASA
Every two years, the Earth passes Mars as they orbit around the Sun, which causes it to appear like it is slowing down and moving in reverse in the sky (aka. “retrograde motion”). Credit: NASA

However, astronomers now calculate the distance to objects in the Solar System using the speed of light. They measure the time it takes for signals to reach spacecraft orbiting other planets. They can bounce powerful radar off planets and measure the time it takes for signals to return. This allows them to measure the distance to planets, like Mars, with incredible accuracy.

Distance Between Earth and Mars:

So, how far away is Mars? The answer to that question changes from moment to moment because Earth and Mars are orbiting the Sun. It also requires a little explanation about the orbital mechanics of each. Both Earth and Mars are following elliptical orbits around the Sun, like two cars travelling at different speeds on two different racetracks.

Sometimes the planets are close together, and other times they’re on opposite sides of the Sun. And although they get close and far apart, those points depend on where the planets are on their particular orbits. So, the Earth Mars distance is changing from minute to minute.

The planets don’t follow circular orbits around the Sun, they’re actually traveling in ellipses. Sometimes they’re at the closest point to the Sun (called perihelion), and other times they’re at the furthest point from the Sun (known as aphelion).

. Credit and copyright: Encyclopedia Britannica
Mars axial tilt and eccentricity as it orbits around the Sun. Credit and copyright: Encyclopedia Britannica

To get the closest point between Earth and Mars, you need to imagine a situation where Earth and Mars are located on the same side of the Sun. Furthermore, you want a situation where Earth is at aphelion, at its most distant point from the Sun, and Mars is at perihelion, the closest point to the Sun.

Earth and Mars Opposition:

When Earth and Mars reach their closest point, this is known as opposition. It’s the time that Mars appears as a bright red star of the sky; one of the brightest objects, rivaling the brightness of Venus or Jupiter. There’s no question Mars is bright and close, you can see it with your own eyes. And theoretically at this point, Mars and Earth will be only 54.6 million kilometers from each other.

But here’s the thing, this is just theoretical, since the two planets haven’t been this close to one another in recorded history. The last known closest approach was back in 2003, when Earth and Mars were only 56 million km (or 33.9 million miles) apart. And this was the closest they’d been in 50,000 years.

Opposition occurs when Mars and Earth line up on the same side of the Sun. The two planets are closest together at that time. Mars opposition occurs on May 22, when the planet will shine at magnitude -2.0 and with an apparent diameter of 18.6 arc seconds, its largest in years. Credit: Bob King
Opposition occurs when Mars and Earth line up on the same side of the Sun. The two planets are closest together at that time. Credit: Bob King

Here’s a list of Mars Oppositions from 2007-2020 (source)

  • Dec. 24, 2007 – 88.2 million km (54.8 million miles)
  • Jan. 29, 2010 – 99.3 million km (61.7 million miles)
  • Mar. 03, 2012 – 100.7 million km (62.6 million miles)
  • Apr. 08, 2014 – 92.4 million km (57.4 million miles)
  • May. 22, 2016 – 75.3 million km (46.8 million miles)
  • Jul. 27. 2018 – 57.6 million km (35.8 million miles)
  • Oct. 13, 2020 – 62.1 million km (38.6 million miles)

2018 should be a very good year, with a Mars looking particularly bright and red in the sky.

Earth and Mars Conjunction:

On the opposite end of the scale, Mars and Earth can be 401 million km apart (249 million miles) when they are in opposition and both are at aphelion. The average distance between the two is 225 million km. When Mars and Earth are at their closest, you have your launch window.

Every 26 months Mars is opposite the Sun in our nighttime sky. Since 1995, Mars has been at such an "opposition" with the Sun seven times. A color composite from each of the seven Hubble opposition observations has been assembled in this mosaic to showcase the beauty and splendor that is The Red Planet. This mosaic of all seven globes of Mars shows relative variations in the apparent angular size of Mars over the years. Mars was the closest in 2003 when it came within 56 million kilometres of Earth. The part of Mars that is tilted towards the Earth also shifts over time, resulting in the changing visibility of the polar caps. Clouds and dust storms, as well as the size of the ice caps, can change the appearance of Mars on time scales of days, weeks, and months. Other features of Mars, such as some of the large dark markings, have remained unchanged for centuries. Credit: NASA/ESA
Since 1995, Mars has been at such an “opposition” with the Sun seven times. A color composite from each of the seven Hubble opposition observations has been assembled in this mosaic to showcase the beauty and splendor that is The Red Planet. Credit: NASA/ESA

Mars and Earth reach this closest point to one another approximately every two years. And this is the perfect time to launch a mission to the Red Planet. If you look back at the history of launches to Mars, you’ll notice they tend to launch about every two years.

Here’s an example of recent Missions to Mars, and the years they launched:

  • MER-A Spirit – 2003
  • MER-B Opportunity – 2003
  • Mars Reconnaissance Orbiter – 2005
  • Phoenix – 2007
  • Fobos-Grunt – 2011
  • MSL Curiosity – 2011

See the trend? Every two years. They’re launching spacecraft when Earth and Mars reach their closest point.

Spacecraft don’t launch directly at Mars; that would use up too much fuel. Instead, spacecraft launch towards the point that Mars is going to be in the future. They start at Earth’s orbit, and then raise their orbit until they intersect the orbit of Mars; right when Mars is at that point. The spacecraft can then land on Mars or go into orbit around it. This journey takes about 250 days.

Communicating with Mars:

With these incredible distances between Earth and Mars, scientists can’t communicate with their spacecraft in real time. Instead, they need to wait for the amount of time it takes for transmissions to travel from Earth to Mars and back again.

Greetings from Mars!   I’m Spirit and I was the first of two twin robots to land on Mars. Unlike my twin, Opportunity, I’m known as the hill-climbing robot.     Artist Concept, Mars Exploration Rovers. NASA/JPL-Caltech
Artist’s impression of the Spirit Rover. One of two rovers that were part of MER program, the other was Opportunity, that began communicating back information that have helped NASA scientists characterize the Martian environment and geological history. NASA/JPL-Caltech

When Earth and Mars are at their theoretically closest point of 54.6 million km, it would take a signal from Earth about 3 minutes to make the journey, and then another 3 minutes for the signals to get back to Earth. But when they’re at their most distant point, it takes more like 21 minutes to send a signal to Mars, and then another 21 minutes to receive a return message.

This is why the spacecraft sent to Mars are highly autonomous. They have computer systems on board that allow them to study their environment and avoid dangerous obstacles completely automatically, without human intervention.

The distance from Earth to Mars is the main reason that there has never been a manned flight to the Red Planet. Scientists around the world are working on ways to shorten the trip with the goal of sending a human into Martian orbit within the next decade.

We have written many articles about the distance between planets here at Universe Today. Here are the distances between Earth and the Sun, Mercury, Venus, the Moon, Jupiter, Saturn, Uranus, Neptune, and Pluto. And here are Ten Interesting Facts about Planet Mars and How Long Does it Take to Get to Mars?

For more information, this website lists every Mars opposition time, from recent past all the way in the far future. You can also use NASA’s Solar System Simulator to see the current position of any object in the Solar System.

Finally, if you’d like to learn more about Mars in general, we have done several podcast episodes about Mars at Astronomy Cast. Episode 52: Mars. We have also done an episode explaining distances, Episode 10: Measuring Distance in the Universe.

Sources:

Jupiter at Opposition by Efrain Morales

Astrophoto: Jupiter at Opposition by Efrain Morales

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This image of Jupiter at opposition was taken by Efrain Morales on October 30, 2011 in Victoria, Aguadilla, Puerto Rico. As seen on the image, “Oval Ba is becoming pale and the barges and festons on the belt regions.”

Opposition is an astronomical event wherein two celestial bodies are in the opposite sides of the sky when viewed from a certain location, in this case, the Earth. During an opposition, the object can be observed almost all night and will be completely illuminated just like a full Moon.

Efrain used the following equipments and specs in taking the image:
LX200ACF 12 in. OTA, F30, CGE mount, PGR Flea3 Ccd, TeleVue 3x barlows, Astronomik RGB filter set.

For more amazing astrophotos, here’s the link to Efrain’s Flickr page.

Want to get your astrophoto featured on Universe Today? Join our Flickr group, post in our Forum or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.