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On February 13 2019, NASA announced that Opportunity - a Mars rover launched in 2003 with an intended longevity of three months - was likely to be dead.

In the wake of this event, and the outpouring of emotion it triggered, I've seen the following claim widely disseminated on social media:

Image of Opportunity overlaid with the caption: "Opportunity's last message to Earth - 'My battery is low and it's getting dark'"

Source of similar claims:

This blog article:

Last June as the dust storm descended upon Opportunity, the rover’s last message essentially said “my battery is low, and it’s getting very dark.”

This echoes the tweet from Jacob Margolis quoted in the 7ABC News and India today articles:

The last message they received was basically, “My battery is low and it’s getting dark.”

Is Opportunity actually capable of such advanced communication skills? Is this someone simply trying to anthropomorphise Opportunity's last contact with the Earth?

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    Folks, we all realize this can't be literally true, but this is not the place to attempt an answer based on this (or pass judgement on the question). Be kind. – Sklivvz Feb 14 at 8:17
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    @Oddthinking I've reverted most of that edit because that's not the question I asked, and it's not the one that two users have answered. I understood on a personal level that Mars rovers are not advanced enough to speak in English, but I asked the question I did because that is the most prevailing idea among the general public, as indicated by the image I included, and that's the perspective it will be approached from by someone with little to no knowledge of the field. It makes no sense to dictate the question based on the answer. – Hashim Feb 14 at 13:14
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    TL;DR: I wrote the question intentionally "naive" and from a standpoint of knowing nothing at all, as that's likely to be the stance of the average member of the general public searching for this information, and that's how you debunk myths. – Hashim Feb 14 at 13:16
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    @Oddthinking No, what's clear is that many people on Skeptics.SE intuitively know that the last message from Opportunity was likely to be a series of digital signals. However, the audience for questions like this isn't the users of this site - it's people in the public domain where the image above came from, and those people don't intuitively know such things. I asked this question so I could have something to point those people to and debunk the myth that Curiosity sends messages in English, which is certainly the case in the larger world outside of SE, and the image is the evidence of that. – Hashim Feb 14 at 14:04
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    @Oddthinking "Please edit it to show that anyone believes the super-naive interpretation of the claim..." I don't think it's out of the realm of possibilities that the creators of the Mars rover could have built-in an Easter egg like this and could have activated it now. They went as far as sending poems to Opportunity (space.stackexchange.com/questions/34180/…), so they may as well have included a mechanism to return something like this. I think it's highly unlikely Opportunity sent such a message literally, but it may have. – Trilarion Feb 14 at 14:47
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Other answers give good technical answers to what the last message would actually have looked like, but I thought it worth tackling the angle of where the quote came from.

Wikipedia cites an article on LAist a Los Angeles local news / blogging site, written by Jacob Margolis.

In it he describes how he coined the phrase:

"My battery is low and it's getting dark."

That's how I felt when I heard that NASA's Opportunity rover mission was coming to an end after 15 years. That Oppy, the rover, was officially dead, and that it had sent back one last alarming communication to Earth before finding its final resting place in Perseverance Valley on the surface of Mars.

On the evening of Feb 12, 2019, he posted a thread of 11 tweets on Twitter, describing the situation, and including various photos from the rover. Tweet number 3 in that thread reads:

The last message they received was basically, "My battery is low and it's getting dark." They hoped that the windy season would clear dust off the solar panels (if that was the problem). Since then they've been pinging her again and again, every way they knew… 3/

This received numerous responses on Twitter, and as it spread, the context was naturally lost. As Margolis continues:

People started talking about it as if they were actually the exact last words that the rover said. The NY Daily News reported it as fact.

JPL contacted me to let me know that they were being inundated with questions about the final message. And while it seemed like most people understood the context within the tweet, many didn't.

In response to queries about whether these really were "the last words", he says:

As NPR's Scott Simon said, it's a "poetic translation."

He then quotes Deputy Project Scientist Abigail Fraeman:

And then it was Sunday, we actually got a communication from the rover and we were shocked. It basically said we had no power left, and that was the last time we heard from it.

...and John Callas, the project manager:

It also told us the skies were incredibly dark, to the point where no sunlight gets through. It's night time during the day.

In both cases, the "it" seems to refer to the rover, anthropomorphising it; this appears to have been Margolis's inspiration to rephrase the message as a quote in the first person.

  • Best answer here – Jason C Feb 18 at 21:40
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    So the status report was more than a "My battery charge level is XX and solar input is YY", but was instead a "There will likely be no chance to send a message later, so send one now to let people know what happened"?: If so, the anthropomorphized version is in some ways less emotional than the reality (since "my battery happens to be low, and it happens to be dark" wouldn't normally have any fatalistic implications, unlike e.g. "Energy generation persistently ineffective; improvement not expected; reserves insufficient to allow further transmissions unless situation spontaneously improves." – supercat Feb 19 at 16:51
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    @supercat, as far as I can tell, "it's getting dark" is the final science transmission: an atmospheric-opacity photograph of the Sun -- or where the Sun would be if dust weren't blocking 99.998% of the light. "My battery is low" is the final engineering-status transmission, which was notification of a low-battery fault. – Mark Feb 19 at 22:30
  • Selecting this as best answer for now, possibly temporarily, to ensure it gets as much upvotes as it deserves. This is the only answer that gets to the crux of the the claim itself and its source, while underscoring just how necessary the question was - it's become clear in the subsequent week since the NASA announcement that the question was needed, but on the 14th February it was far less clear to most and was an uphill struggle just to keep it open. – Hashim Feb 20 at 2:43
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    @supercat Not even "my battery charge level is XX and solar input is YY". The message was "my battery charge level is XX. Here's a picture of the sky" The opacity values were calculated on Earth, the rover didn't analyze them. – Rekesoft Feb 22 at 11:54
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From a NASA blog post made the day after contact was lost:

The dust storm that is affecting Opportunity has greatly intensified.

The atmospheric opacity (tau) over the rover has increased to a record 10.8 on Sol 5111 (June 10, 2018). Power levels on the rover have dropped to a record low of ~22 watt hours. As expected, Opportunity has tripped a low-power fault and gone silent. A 72-hour spacecraft emergency was declared on the afternoon of Sol 5111 (June 10, 2018), anticipating the low-power fault.

High atmospheric opacity means that the atmosphere is blocking a lot of sunlight, making it dark. Future estimates of atmospheric opacity are far less precise, so we can conclude that the measurement of tau was transmitted from the rover rather than another source.

From an interview given later:

"We are looking at an incredibly small amount of sunlight – .002 percent of the normal sunlight that we would expect to see," Bill Nelson from NASA’s Jet Propulsion Laboratory (JPL), chief of the Opportunity mission’s engineering team, told Mashable. "If you were there, it would be late twilight. Your human eye would still be able to make out some features, but it would be very dark."

The darkness and record low battery are consistent with the claim. The last image sent by opportunity was static and blackness. The filename indicates it was taken at 4:24 PM UTC.

Opportunity definitely transmitted the information in the claim on its last day. I do not know if it transmitted anything else in a separate transmission afterwards. It most certainly did not transmit a plain English message ready to be memed, but rather a technical status update that NASA's bloggers interpreted for us, and then was reinterpreted into the meme.

As a personal note, if I am on my deathbed and I say something meaningful and wise, and then I follow it up with a mundane comment right before I die, please remember the wise thing as my last words.

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    The last 3 SOL image sets (5107, 5109, 5111) contain only "static" or black images. Black spaces typically mean partial data has arrived, but Opportunity will fill in the rest of the data as soon as possible. The "static" is possibly haze from a dust storm, since we know the opacity was very high. – CJ Dennis Feb 15 at 2:01
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    Thank you for resisting the temptation to put a simple "yes" or "no" in your answer and instead focusing on the reality of what happened. – jpmc26 Feb 15 at 3:25
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    Bob, that is a very good request at the end of your answer. – The Mattbat999 Feb 17 at 14:23
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    .... unless your final words on your deathbed are "Daisy, Daisy..." Then we're holding you to them! – Cort Ammon Feb 17 at 22:57
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Opportunity does not literally speak English, so no such message was expressed in those terms. However, Opportunity did communicate the information that it had a low battery and it was dark outside.

The rover's flight software outputs a variety of data formats (summarized in this paper) ranging from "event reports" to telemetry to binary data produced by the spacecraft's subsystems (including imagery from cameras and other research products). The result of all of that is downlinked to earth and then processed on the ground by different teams into human-readable output. While there is a great deal of public data available for download, I don't believe this applies to the raw transmissions from the rover, but you can see the ACSV format some of the engineering data is processed into. Scientists then process and review that data and write things about it in English, anything from technical reports ("a measured tau of 10.8") to the more poetic "my battery is low, and it’s getting very dark."

Here's the Sol 5110-5114 MER B Downlink Report from mission management conveying information about the last transmissions received from the rover:

Mission Manager

* Tau Value is NOT a Typographical Error *

Overall Assessment Opportunity is currently in the midst of a severe dust storm though all subsystems are still operating as expected in RAM mode as of the Sol 5111 UHF pass. Solar array energy is approximately 22 W-hrs, with a measured tau of 10.8. This Tau measurement is the highest ever recorded from a ground station on the planet Mars. Dust factor was previously estimated at 3.27 as of Sol 5108.

With analysis from the data from the Sol 5111 downlink, we expected the rover to enter a low power fault mode very soon after that point in time. Since then, there have been no beeps nor fault windows detected during DSN coverage periods. This behavior is fully in line with array energy expectations, as Opportunity will use deep sleep during such times. We are now waiting for the skies above Opportunity to clear enough for the solar energy to support the fault communications windows (which will send signals to Earth). The team has suspended nominal sequence operations, and we are listening every day for Opportunity to talk to us via one of the fault windows. Thermal predictions carry a positive medium to long term message, whether it takes several sols or several weeks for the storm to weaken and let the sun through. We expect no thermal damage to the batteries or computer systems, and every sol is one closer to summer warmth. Obviously, the team is concerned. But, all of the data and our knowledge indicate that Opportunity is likely to be doing more geological experiments during the upcoming Martian summer, helping unwrap the mysteries of Endeavour crater. Until then, our current mission phase is one of patience and readiness.

Opportunity did not drive during this period.

As can be shown in this chart, 22 W-hrs is a very low value for energy collected from the solar array as compared to previous periods. At this time, the scientists considered "a low power fault" to be "inevitable" (note though that "There is no danger to the spacecraft going into a low power fault. The only danger is the temperature getting too cold and damaging the battery or the instruments.") The tau value (atmospheric opacity) is the highest ever recorded, so high that the report includes a prominent note alerting readers that it's not a typo. The rover does not calculate this value itself; it takes a picture of the sun through a solar filter, and scientists process that image on the ground to determine the numerical value. In other words, the spacecraft reported data indicating low energy and darkness.

Opportunity also sent back a final Pancam image at that time. It's the image that was used to calculate that tau value. It's very dark: static

Thanks Oppy!

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    How do you know that the image was used to calculate the Tau value? – BobTheAverage Feb 14 at 15:31
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    "It's getting dark" is a pretty good summation of that image. A Tau of 10.8 means that 99.998% of the Sun's light is being blocked by dust. – Mark Feb 15 at 2:21
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    @RichieFrame Where are you getting that filename? My link to it, (mars.nasa.gov/mer/gallery/all/opportunity_p5111_text.html) shows that the filename is a cryptic string of characters. When decoded this string indicates that the pancam was using the solar filter, which is 440 nm, which is blue not IR. – BobTheAverage Feb 15 at 3:20
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    @BobTheAverage The filename is sol5111_pancam_tau.jpg. That's listed in the analyst's notebook and included as an attachment to the mission manager's report, which describes it as "Sol 5111 Pancam Tau (10.8)" If I've misidentified the image, just let me know. – Zach Lipton Feb 15 at 5:17
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    @BobTheAverage by IR filter, I mean IR block, which kicks out the red and IR, letting yellow, green, and blue through. Max solar energy output is around 450nm, so having the IR filter be most transparent around that wavelength is optimal (as long as it is not 434nm) – Richie Frame Feb 15 at 8:21
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This Metro article cites a tweet by Keri Bean, an engineer who worked on the opportunity mission who had Oppy’s final measurement tattooed on her arm.

This tattoo means more to me than just Oppy. Of course, the biggest significance is this is Oppy’s final measurement. I studied tau (atmospheric optical depth) as a student researcher. Don’t worry, I consulted my advisor on the value before committing to the ink

As others have said, oppy doesn’t speak plain English, transmissions are simply packets of data, so the final message would most likely be as per the image of the tattoo:

τ=10.8

enter image description here
@PlanetaryKeri

This could then be interpreted to the message in the meme.

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    Aren’t the other answers stating that tau is calculated by mission control, not by Oppy? – Andrew Grimm Feb 17 at 10:40
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    @AndrewGrimm one answer does but I’ve seen no definite source for the claim. – Notts90 Feb 17 at 14:40
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    It's also very unlikely that the transmission included a unicode tau character and an equals sign, or decimal digits. But Descartes never said 'I think therefore I am' either. – Pete Kirkham Feb 18 at 13:05
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    Wouldn't it be funny if they issued a correction and it was actually 10.7? – Jason C Feb 18 at 21:36
  • @JasonC a very frustrating rounding error!! – Notts90 Feb 18 at 22:48

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