Opportunity, also known as MER-B (Mars Exploration Rover – B) or MER-1, and nicknamed Oppy,^[8][9] is a robotic rover that was active on Mars from 2004 to 2018.^[2] Launched on July 7, 2003, as part of NASA's Mars Exploration Rover program, it landed in Meridiani Planum on January 25, 2004, three weeks after its twin Spirit (MER-A) touched down on the other side of the planet.^[10] With a planned 90-sol duration of activity (slightly more than 90 earth days), Spirit functioned until getting stuck in 2009 and ceased communications in 2010, while Opportunity was able to stay operational for 5353 sols after landing, maintaining its power and key systems through continual recharging of its batteries through solar power, and hibernating during events such as dust storms to save power. This careful operation allowed Opportunity to exceed its operating plan by 14 years, 295 days (in Earth Time), 55 times its designed lifespan. By June 10, 2018, when it last contacted NASA,^[11][12] the rover had traveled a distance of 45.16 kilometers (28.06 miles).^[7]

Mission highlights included the initial 90-sol mission, finding extramartian meteorites such as Heat Shield Rock (Meridiani Planum meteorite), and over two years of exploring and studying Victoria crater. The rover survived less severe dust storms and in 2011 reached Endeavour crater, which has been described as a "second landing site".^[13] The Opportunity mission is considered one of NASA's most successful ventures.^[14]

Due to the 2018 dust storms on Mars, Opportunity ceased communications on June 10 and entered hibernation on June 12, 2018. It was hoped it would reboot once the weather cleared,^[15] but it did not, suggesting either a catastrophic failure or that a layer of dust has covered its solar panels. NASA hoped to reestablish contact with the rover, citing a windy period that could potentially clean off the solar panels of the rover.^[16] On February 13, 2019, NASA officials declared that the Opportunity mission was complete, after the spacecraft failed to respond to repeated signals sent since August 2018.^[17]

Mission overview

Collectively, the Opportunity and Spirit rovers were part of the Mars Exploration Rover program in support of the long-term Mars Exploration Program. The Mars Exploration Program's four principal goals were to determine if the potential for life exists on Mars (in particular, whether recoverable water can be found on Mars), to characterize the Mars climate and its geology, and then to prepare for a potential human mission to Mars. The Mars Exploration Rovers were to travel across the Martian surface and perform periodic geologic analyses to determine if water ever existed on Mars as well as the types of minerals available, as well as to corroborate data taken by the Mars Reconnaissance Orbiter.^[18]

Spirit and Opportunity were launched a month apart, on June 10 and July 7, 2003, and both reached the Martian surface by January 2004. Both rovers were designed with an expected 90 sols (92 Earth days) lifetime, but each significantly lasted much longer than expected. Spirit's mission lasted 20 times longer than this expected lifetime, and its mission was declared ended on May 25, 2011, after it got stuck in soft soil and expended its power reserves trying to free itself. Similarly, Opportunity was able to last 55 times longer than the 90 sol lifetime, operating for 5498 days from landing to mission end. An archive of weekly updates on the rover's status can be found at the Opportunity Update Archive.^[19]

From its initial landing, by chance, into an impact crater amidst an otherwise generally flat plain, Opportunity successfully investigated soil and rock samples and took panoramic photos of its landing site. Its sampling allowed NASA scientists to make hypotheses concerning the presence of hematite and past presence of water on the surface of Mars. Following this, it was directed to travel across the surface of Mars to investigate another crater site, Endurance crater, which it investigated from June to December 2004. Subsequently, Opportunity examined the impact site of its own heat shield and discovered an intact meteorite, now known as Heat Shield Rock, on the surface of Mars.

From late April to early June 2005, Opportunity was perilously lodged in a sand dune, with several wheels buried in the sand. Over a six-week period Earth-based physical simulations were performed to decide how best to extract the rover from its position without risking a permanent immobilization of the valuable vehicle. Successful maneuvering a few centimeters at a time eventually freed the rover, which resumed its travels.

Opportunity was directed to proceed in a southerly direction to Erebus crater, a large, shallow, partially buried crater and a stopover on the way south towards Victoria crater, between October 2005 and March 2006. It experienced some mechanical problems with its robotic arm.

In late September 2006, Opportunity reached Victoria crater and explored along the rim in a clockwise direction. In June 2007 it returned to Duck Bay, its original arrival point; in September 2007 it entered the crater to begin a detailed study. In August 2008, Opportunity left Victoria crater for Endeavour crater, which it reached on August 9, 2011.^[20]

Here at the rim of the Endeavour crater the rover moved around a geographic feature named Cape York. The Mars Reconnaissance Orbiter had detected phyllosilicates there, and the rover analyzed the rocks with its instruments to check this sighting on the ground. This structure was analyzed in depth until summer 2013. In May 2013 the rover was heading south to a hill named Solander Point.

Opportunity's total odometry by June 27, 2016 (sol 4417), was 42.85 km (26.63 mi), while the dust factor is 0.725.^[21] Since January 2013, the solar array dust factor (one of the determinants of solar power production) varied from a relatively dusty 0.467 on December 5, 2013 (sol 3507), to a relatively clean 0.964 on May 13, 2014 (sol 3662).^[22]

In December 2014, NASA reported that Opportunity was suffering from "amnesia" events in which the rover failed to write data, e.g. telemetry information, to non-volatile memory. The hardware failure was believed to be due to an age-related fault in one of the rover's seven memory banks. As a result, NASA had aimed to force the rover's software to ignore the failed memory bank;^[23] amnesia events continued to occur, however, which eventually resulted in vehicle resets. In light of this, on Sol 4027 (May 23, 2015), the rover was configured to operate in RAM-only mode, completely avoiding the use of non-volatile memory for storage.^[24]

End of mission

In early June 2018, a large global-scale dust storm developed, and within a few days the rover's solar panels were not generating enough power to maintain communications, with last contact on June 10, 2018.^[5] NASA stated they did not expect to resume communication until after the global dust storm subsided,^[25] but the rover kept silent even after the storm ended in early October,^[25] suggesting either a catastrophic failure or a layer of dust covered its solar panels.^[26] The team remained hopeful that a windy period between November 2018 and January 2019 might clear the dust from its solar panels, as had happened before.^[26] Wind was detected nearby on January 8, and on January 26 the mission team announced a plan to begin broadcasting a new set of commands to the rover in case its radio receiver failed.^[27] More than 835 recovery commands were transmitted over the next 11 days, but no response was generated,^[28] and after a final attempt to make contact on February 12,^[29] NASA officials held a February 13 press conference to declare an official end to the mission. NASA associate administrator Thomas Zurbuchen stated, "It is therefore that I am standing here with a deep sense of appreciation and gratitude that I declare the Opportunity mission is complete."^[30]

As NASA ended their attempts to contact the rover, the last data sent was the song "I'll Be Seeing You" performed by Billie Holiday.^[31]

Objectives

The scientific objectives of the Mars Exploration Rover mission were to:^[33]

• Search for and characterize a variety of rocks and soils that hold clues to past water activity. In particular, samples sought include those that have minerals deposited by water-related processes such as precipitation, evaporation, sedimentary cementation or hydrothermal activity.
• Determine the distribution and composition of minerals, rocks, and soils surrounding the landing sites.
• Determine what geologic processes have shaped the local terrain and influenced the chemistry. Such processes could include water or wind erosion, sedimentation, hydrothermal mechanisms, volcanism, and cratering.
• Perform calibration and validation of surface observations made by Mars Reconnaissance Orbiter instruments. This will help determine the accuracy and effectiveness of various instruments that survey Martian geology from orbit.
• Search for iron-containing minerals, identify and quantify relative amounts of specific mineral types that contain water or were formed in water, such as iron-bearing carbonates.
• Characterize the mineralogy and textures of rocks and soils and determine the processes that created them.
• Search for geological clues to the environmental conditions that existed when liquid water was present.
• Assess whether those environments were conducive to life.

During the next two decades, NASA will continue to conduct missions with other spacecraft to address whether life ever arose on Mars. The search begins with determining whether the Martian environment was ever suitable for life. Life, as we understand it, requires water, so the history of water on Mars is critical to finding out if the Martian environment was ever conducive to life. Although the Mars Exploration Rovers did not have the ability to detect life directly, they offered very important information on the habitability of the environment in the planet's history.

Design and construction

Spirit and Opportunity are twin rovers, each a six-wheeled, solar-powered robot standing 1.5 meters (4.9 ft) high, 2.3 meters (7.5 ft) wide, and 1.6 meters (5.2 ft) long and weighing 180 kilograms (400 lb). Six wheels on a rocker-bogie system enable mobility. Each wheel had its own motor, the vehicle was steered at front and rear and was designed to operate safely at tilts of up to 30 degrees. Maximum speed was 5 centimeters per second (2.0 in/s) although average speed is about a fifth of this (0.89 centimeters per second (0.35 in/s)). Both Spirit and Opportunity have pieces of the fallen World Trade Center's metal on them that were "turned into shields to protect cables on the drilling mechanisms".^[34][35]

Solar arrays generated about 140 watts for up to fourteen hours per Martian day (sol) while rechargeable lithium ion batteries stored energy for use at night. Opportunity's onboard computer used a 20 MHz RAD6000 CPU with 128 MB of DRAM, 3 MB of EEPROM, and 256 MB of flash memory. The rover's operating temperature ranged from −40 to +40 °C (−40 to 104 °F) and radioisotope heaters provided a base level of heating, assisted by electrical heaters when necessary.^[36] A gold film and a layer of silica aerogel provided insulation.

Communications depended on an omnidirectional low-gain antenna communicating at a low data rate and a steerable high-gain antenna, both in direct contact with Earth. A low gain antenna was also used to relay data to spacecraft orbiting Mars.

Fixed science/engineering instruments included:

• Panoramic Camera (Pancam) – examines the texture, color, mineralogy, and structure of the local terrain.
• Navigation Camera (Navcam) – monochrome with a higher field of view but lower resolution, for navigation and driving.
• Miniature Thermal Emission Spectrometer (Mini-TES) – identifies promising rocks and soils for closer examination, and determines the processes that formed them.
• Hazcams, two B&W cameras with 120 degree field of view, that provide additional data about the rover's surroundings.

The rover arm held the following instruments:

• Mössbauer spectrometer (MB) MIMOS II – used for close-up investigations of the mineralogy of iron-bearing rocks and soils.
• Alpha particle X-ray spectrometer (APXS) – close-up analysis of the abundances of elements that make up rocks and soils.
• Magnets – for collecting magnetic dust particles
• Microscopic Imager (MI) – obtains close-up, high-resolution images of rocks and soils.
• Rock Abrasion Tool (RAT) – exposes fresh material for examination by instruments on board.

The cameras produced 1024-pixel by 1024-pixel images, the data is compressed with ICER, stored, and transmitted later.

The rover's name was chosen through a NASA sponsored student essay competition.

Opportunity was 'driven' by several operators throughout its mission, including JPL roboticist Vandi Verma who also cowrote the PLEXIL command language used in its software.^[37]

Power

The rover used a combination of solar cells and a rechargeable chemical battery.^[39] This class of rover has two rechargeable lithium batteries, each composed of 8 cells with 8 amp-hour capacity.^[40] At the start of the mission the solar panels could provide up to around 900 watt-hours to recharge the battery and power system in one Sol, but this could vary due to a variety of factors.^[39] In Eagle crater the cells were producing about 840 watt-hours, but by Sol 319 in December 2004, it had dropped to 730 watt-hours.^[41]

Like Earth, Mars has seasonal variations that reduce sunlight during winter. However, since the Martian year is longer than that of the Earth, the seasons fully rotate roughly once every 2 Earth years.^[42] By 2016, MER-B had endured seven Martian winters, during which times power levels drop which can mean the rover avoids doing activities that use a lot of power.^[42] During its first winter power levels dropped to under 300 watt-hours per day for two months, but some later winters were not as bad.^[42]

Another factor that can reduce received power is dust in the atmosphere, especially dust storms.^[43] Dust storms have occurred quite frequently when Mars is closest to the Sun.^[43] Global dust storms in 2007 reduced power levels for Opportunity and Spirit so much they could only run for a few minutes each day.^[43] Due to the 2018 dust storms on Mars, Opportunity entered hibernation mode on June 12,^[44][45] but it remained silent after the storm subsided in early October.^[25]

Examples

Examples of watt-hours per sol collected by the rover:^[46]

Launch

Opportunity's launch was managed by NASA's Launch Services Program. This was the first launch of the Delta II Heavy. The launch period went from June 25 to July 15, 2003. The first launch attempt occurred on June 28, 2003, but the spacecraft launched nine days later on July 7, 2003, due to delays for range safety and winds, then later to replace items on the rocket (insulation and a battery). Each day had two instantaneous launch opportunities. On the day of launch, the launch was delayed to the second opportunity (11:18 p.m. EDT) in order to fix a valve.^[47]

Landing

On January 25, 2004, the airbag-protected landing craft settled onto the surface of Mars in the Eagle crater.

Heat shield impact site

In late December 2004, Opportunity reached the impact site of its heat shield, and took a panorama around Sol 325.^[48]

Scientific findings

Opportunity has provided substantial evidence in support of the mission's primary scientific goals: to search for and characterize a wide range of rocks and soils that hold clues to past water activity on Mars. In addition to investigating the water, Opportunity has also obtained astronomical observations and atmospheric data.

Honors

Honoring Opportunity's great contribution to the exploration of Mars, an asteroid was named Opportunity: 39382 Opportunity.^[49] The name was proposed by Ingrid van Houten-Groeneveld who, along with Cornelis Johannes van Houten and Tom Gehrels, discovered the asteroid on September 24, 1960. Opportunity's lander is Challenger Memorial Station.^[50]

On July 28, 2014, it was announced that Opportunity, having traversed over 40 km (25 mi), had become the rover achieving the longest off-world distance, surpassing the previous record of 39 km (24 mi) on the Moon by Lunokhod 2.^[51][52]

On March 24, 2015, NASA celebrated Opportunity having traveled the distance of a marathon race, 42.195 kilometers (26.219 mi), from the start of Opportunity's landing and traveling on Mars.^[53]

Superlatives

Steepest slope

Highest elevation

On Sol 3894 (January 6, 2015), Opportunity reached the summit of "Cape Tribulation," which is 443 feet (135 meters) above "Botany Bay" level and the highest point yet reached by the rover on western rim of Endeavour Crater according to NASA.^[25]

Driving distance

Images

The rover could take pictures with its different cameras, but only the PanCam camera had the ability to photograph a scene with different color filters. The panorama views are usually built up from PanCam images. By February 3, 2018, Opportunity had returned 224,642 pictures.^[55][56]

Views

Panoramas

A selection of panoramas from the mission:

Microscopic images

From orbit

Area maps

Traverse maps

An example of a rover traverse map featuring a line showing path of the rover, and mission sols, which are Mars days counted from its landing and typical of Mars surface mission time reporting. Topographic lines and various feature names are also common

See also