Something catastrophic had to have happened to have changed the ancient warm and wet Mars into the modern cold and dry Mars. MAVEN will investigate our leading hypothesis which is that the Solar Wind eroded away the atmosphere over billions of years. The MAVEN mission launches on Nov. 18 and will go into orbit around Mars in Sept. 2014. Video summary:

Other resources:


Answering questions today on the maven2Mars account is Jared Espley, space scientist at NASA's Goddard Space Flight Center in Greenbelt, MD and a member of the MAVEN science team. He's happy to answer questions about MAVEN, Mars, and NASA. Espley twitter account is @JaredEspley, MAVEN's Twitter account is @MAVEN2Mars, and NASA Goddard is @NASAGoddard

Edit: 3pm ET Ok, Jared here signing off.

Edit2: 8:45pm ET Ok, Jared back here for a bit to answer a few more questions and fix some typos.

Edit3: 10pm ET Signing off again! Thanks for all the questions. Sorry to those I didn't get to. If I get a chance I'll come by through the weekend to answer any straggler questions if my colleagues don't catch them. Go Mars!

Comments: 466 • Responses: 71  • Date: 

bunnytrox70 karma

What do you think will be the greatest finding of the mission?

maven2mars107 karma

Main goal of the mission is to discover what happened to the atmosphere of Mars. How it went from a warm, wet place with the possibility of life to the dry, cold desert of today. So if we verify our hypothesis that the Solar Wind stripped away most of the atmosphere then that will be our most important finding.

EvilTech515054 karma

If the real reason happens to be giant alien spider monsters, can you convince nasa to bring a few back? I'm working on this Darpa project you see and I need an edge over the competition. :D

maven2mars75 karma

Roger, roger.

EsotericHabit32 karma

What sort of evidence would help confirm your hypothesis?

maven2mars64 karma

We're going to do our best to count all the particles escaping from the planet at any given moment in space and time and then add that all up and see if it makes enough escaping atmosphere over 4 billion years.

Maximus-the-horse29 karma

How on earth do you count all the particles?

maven2mars34 karma

We have particle spectrometers (detectors that tell what the energies and masses are of incoming particles) that cover most all of the energy ranges. Anything lower than our energy range isn't likely to escape and anything higher is kinda ridiculous and probably a passing galactic ray. We count how many particles come in per second per energy per mass per direction per location and get an estimate for the number flowing at that moment in time and that location. Then we try estimate that across the whole region. Of course things change so that's why we have to accumulate statistics. So we don't literally capture every particle but we create an observational net to try effectively capture them.

DictatorDono54 karma

Had to be asked.

Do you play Kerbal Space Program?

maven2mars63 karma

I do not. I am a gamer. But somehow haven't made it KSP yet. Been playing some L4D2 with friends recently and finally beat Assassin's Creed II (!). My poor games-to-play list is ever growing.

BoobooManMan8 karma

Do you play League of Legends?

maven2mars23 karma

No, but it looks interesting.

serpentson3 karma

League is good for beginners to the genre. Dota is less noob friendly, but once learned I find that the games are more rewarding. HoN is more difficult than leage, but lends itself to faster games, or so I hear.

I would recommend getting into one, and sticking to it. Trying to learn a second well... First, you explore an alien planet (I assume you can imagine this), then, you choose to explore a different alien planet of roughly the same size. Its extremely different. The games are the same genre, but very different.

maven2mars11 karma

I used to play SC2 a lot. Got to Diamond once I think. Fun but I don't have the time to devote to that these days.

KhabaLox51 karma

Woohoo! I know an internet celebrity.

Go Jared! Good luck with the launch and your mission.

EDIT: I guess I should ask a question. What are the chances you'll make our D&D session tonight?

maven2mars52 karma

Hey man! Was hoping to see if you popped in. We'll see about gaming tonight.

alice_8833 karma

What class do you play?

maven2mars29 karma

In this campaign an illusionist.

perche45 karma

What makes you think Mars was once warm and wet?

maven2mars90 karma

We clearly see dry river beds all across the surface. Plus lots of rocks and minerals that only form in the presence of standing water. So there had to be long standing liquid water. To have liquid water, you would have to have a much warmer and thicker atmosphere. But that seems to be long gone.

zerogee44 karma

If Earth is able to hold on to its atmosphere, why couldn't Mars?

maven2mars76 karma

Earth has a global planetary magnetic field. This makes a magnetosphere which causes the ionized Solar Wind to be mostly diverted around the planet (magnetic fields move charged, or ionized particles). Mars lacks this planetary magnetic field, hence lacks a magnetosphere, and hence is directly impacted by the Solar Wind. Over billions of years we think that Mars' atmosphere might have been eroded away.

rabootcha39 karma

Theoretically speaking, is there a way for us to generate a planet-wide magnetic field on Mars?

maven2mars27 karma

Sure, heat the core back up (if it's in fact solid instead of molten) and then get it swirling again. The seed magnetic field of the Solar Wind will do the rest and viola you'll have a planetary dynamo once again. For long term stability you might also need plate tectonics to keep things churning and swirling. How long do you need the magnetic field for?

zerogee35 karma

Is there another way Mars could have lost its atmosphere, besides being stripped off by the solar wind?

maven2mars52 karma

Definitely. It could have condensed out and be frozen deep in the ground. However, we don't see a lot of evidence of this. In fact, we see evidence that the lighter parts of the atmosphere (e.g. lighter isotopes) are preferentially gone from the atmosphere (vs. the heavier ones). So we think the solar wind stripping is definitely the best hypothesis at the moment. But it's great in science to test things like we're planning.

PounderMcNasty31 karma

What question would you like to ask an alien?

maven2mars68 karma

How'd you get here?

maven2mars61 karma

You aren't going to eat me are you?

geo_carter28 karma

I wonder if you could elaborate on why MAVEN will be in such an elliptical orbit? Is there a benefit from having apogee as high as 3,728 miles?

maven2mars39 karma

Yes, we're exploring how the Solar Wind affects the upper atmosphere of Mars. So we want to measure things directly in the ionosphere but also way out in the Solar Wind. Our elliptical orbit lets us samples both of those regions. In fact, our orbit is like bit net around the planet, letting us capture possibly escaping particles throughout the Mars interaction region.

funky4921 karma

Was there any instrumentation that was wanted to be included on the MAVEN mission but had to be left out?

maven2mars37 karma

We are fortunate to have a very comprehensive instrument suite for studying our objective (the upper atmosphere of Mars and its interaction with the Solar Wind). Scientists can always use more data, better instruments, etc. but in this case honestly very little comes to mind. However, it would be fantastic if we had another spacecraft with similar instruments to monitor the Solar Wind when we're close to the planet and vice versa. The Chinese mission to Mars had a magnetometer on it which would have been great but sadly the mission didn't make it out of Earth orbit along with its Russian counterpart. I personally hope that another magnetometer will make it into orbit around Mars while MAVEN is still there.

funky4914 karma

Do you know if India's MOM mission has a magnetometer?

maven2mars25 karma

MOM does not. There was some discussion early on about the possibility but I'm not sure how they selected their instruments in the end.

Universu18 karma

How long will maven fly around mars? Would it complement MRO, Odyssey, and Express as relay for MSL? Will it be racing with MOM/Mangalyaan?

maven2mars29 karma

MAVEN's main mission is 1 Earth year. We certainly hope to last longer than that. Yes, we are a backup relay for the rovers (both MSL and Opportunity) but MRO and the others will continue to be the main relays for as long as they last. We're certainly not racing but it is neat that we're both arriving around the same time. Obviously, planetary dynamics only allows certain time periods for launches but still it's cool that there are two missions this time.

ocelot199018 karma

Do you believe it is better from a cost aspect that we keep sending unmanned instruments and rovers to gather scientific data versus investing in a manned mission. Also, do you believe sending people to Mars would allow us to gain more significant data on a scale that makes it worth the time and cost?

maven2mars46 karma

I honestly think that having both the human part and the robotic part of the space exploration program is important. Sending robots can be generally cheaper which is good for science (although some things are very easy for humans like picking up rocks and checking them out for fossils). But ultimately, sending humans to explore space is an act of deep inspirational power which transcends purely scientific inquiry.

happinesswins21 karma

"But ultimately, sending humans to explore space is an act of deep inspirational power which transcends purely scientific inquiry." Beautiful, Jared, thank-you...

maven2mars19 karma

Thanks -- it's hard to type fast and think poetically at the same time. :)

Universu16 karma

What is the rationale for the Sea Gull shape of its solar panel?

maven2mars20 karma

I (Jared) don't know. I'll ask my colleagues and if we can we'll come back to this question.

Universu9 karma

Thanks. Just curious about its unique shape

maven2mars21 karma

I'm speculating that its for aerodynamic reasons since as part of our science objectives (study upper atmosphere) we actually dip in fairly close (~125 km altitude). It may be the case that there is enough drag that it needs to aerodynamically shaped correctly. But expertise is not on aerodynamics so hopefully we'll get a more definitive answer.

rickydelap15 karma

What is the most complicated thing in doing these kind of projects?

maven2mars36 karma

The most complicated thing is the complication. Seriously, something like this has so many people, so many parts, it's very hard to keep track. Those at the highest level have to trust those below but still someone always has to be keeping an eye for system level questions. In that, it's like any other large project. Except Space!

not-just-yeti14 karma

As the team prepared the mission, what was the biggest heart-lurching problem you experienced? What incident makes you laugh, looking back on it now?

maven2mars25 karma

The government shut-down was a little anxiety causing since it came so close to our launch date and we have a very fixed launch window (Mars moves away on its orbit and won't come back for another 2 years).

gaseouscloud12 karma

Do you think there is a chance we could terraform Mars so us Earth-bound folks can take a trip there? Or will the solar wind put pay to that?

maven2mars19 karma

If terraforming ever happens, then it'll take hundreds, thousands? of years. So sadly, no terraforming in our lifetimes. But certainly it's plausible to send humans there. The Solar Wind's erosion is very gradual so it itself is not directly dangerous to humans. Solar radiation, cold, and the lack of oxygen in the atmosphere are bigger problems. Oh and food.

issamaysinalah11 karma

Can you write my nome on the rocket ?

maven2mars27 karma

Sadly, you missed your opportunity. There is a DVD with thousands of names going to Mars. The DVD got strapped on to the outside of the spacecraft a few weeks and previously there was a campaign to get people to sign up to add their name. I'm sure future space missions will do similar programs though so keep your eyes pealed. Or find a sneaky friend who works in the cleanroom and has a cleanroom sharpie.

maven2mars21 karma

Over 100,000 names, 15,000 haiku, and 300+ pieces of student artwork will accompany MAVEN on its journey to investigate the Martian upper atmosphere.

Universu11 karma

What is the next Mars Orbiter after MAVEN?

maven2mars17 karma

The next mission is Insight which will a geophysical stationary lander. Then European 2018 Exomars rover (and telecom orbiter?). Then a NASA 2020 rover. So I think the next Mars orbiter is the 2018 European one.

Universu9 karma

Is there a chance that Insight and Curiosity will be able to meet on Mars? Thanks for the info:)

maven2mars15 karma

Landing site for Insight hasn't been decided yet but very, very likely no. Insight is stationary and I doubt MSL would travel the 100-1000s of km to get to Insight. But it's fun to think about.

NASAGoddard10 karma

While Jared will be busy with MAVEN activities up until launch - NASAGoddard and MAVEN2Mars will be checking back to answer more questions throughout the weekend. GO MAVEN!

maven2mars15 karma

I'm still here! Just kidding. I probably should sign off soon. But the questions have been great. I'll try to pick up some straggler questions later if the NASAGoddard account hasn't already picked them up. Any last questions for me before I sign off?

Universu10 karma

Will the data collected be helpfull, in case a plan to terraform or engineer a new mars atmosphere be initiated?

maven2mars18 karma

In the very long term, yes. Any attempts to terraform a planet would require a deep understanding of how planets work and how that specific planet works. So understanding this part of the Martian system would be important.

Sir_Tibbles9 karma

What are you looking for when trying to identify if it was solar winds? Are missing isotopes as mentioned in the video the only way to tell? Also can you explain what magnetic umbrellas are, and what causes them?

maven2mars8 karma

The isotopes are a good clue but in essence we're going to do our best to count all the particles escaping from the planet at any given moment in space and time and then add that all up and see if it makes enough escaping atmosphere over 4 billion years.

The magnetic umbrellas are caused by strong crustal magnetic fields. Even though Mars doesn't have a planetary sized magnetic field, it does have these patches that are strongly magnetized. In those regions, the Solar Wind can almost be diverted in just that little region, like a mini-magnetosphere.

ajmeN9 karma

Just wanted to say that I love your work at NASA & with MAVEN, thank you and the rest for everything!

maven2mars12 karma

Awesome. It's pretty fun most of the time.

io_la6 karma

Do you think that there will be a time when people live and work on Mars?

I teach Physics (and Maths) and sometimes pupils ask why it's necessary e.g. to examine Mars to buy a multi billion € particle accelerator "when nothing useable comes out of it". What is your answer, or don't people dare to ask you that question ;-)

maven2mars10 karma

Yes, I think that there will be a time that humans live and work on Mars (and throughout the Solar System). But I'm human optimistic and I certainly won't speculate when exactly.

The justification for science generally is the tremendous advance to society as we learn about the world, how it works, and how to use that knowledge for the benefit of society. As to space exploration, science is part of it but it also comes to down to a question of human nature -- we explore because it gives us joy.

BoobooManMan6 karma

How soon can we have a functional Dyson sphere?

maven2mars10 karma

You could take the amount of global energy usage and extrapolate into the future to see when we would have enough energy usage to make the Dyson sphere. You'd have to decide if your extrapolation would be linear (goes up normally over time), or if would up more or less quickly than the past.

Zazenroshi5 karma

What do you know about the Mars One project? Do you think their timeline is feasible or their objective possible? Best of luck with the mission, I hope your research will further humanity's efforts in learning as much as possible about our neighbor Mars, and hopefully going there.

maven2mars4 karma

It's very expensive to send people to Mars so there would have to be a tremendous amount of support for any organization to do it. That said, I certainly wish all space explorers the best of luck.

want-to-say-this5 karma

How realistic and how rapid would plant life introduced to the planet by able to self replicate and spread across the planet, this is under the assumption that there would be enough water to keep the plants alive as they struggle to spread and then cause a snowball effect and progressively convert the non oxygen laden environment into a higher concentration from photosynthesis?

maven2mars9 karma

I don't have any quantitative estimates but the main problem would be nutrients and cold I think. For terraforming, you'd probably need to start with the climate first and then think about adding plant life. Or maybe some microbes. But I'm just making this up as I go. Plasma physicists aren't necessarily the best qualified to talk about plants, even space plants.

jccwrt5 karma

Since MAVEN will be dipping into the Martian atmosphere, would orbital decay put any limits on possible mission extentions?

maven2mars9 karma

Yes, we have enough fuel for several deep dips (~125 km) and at least one Earth year of our normal operations (~150 km). We then have plenty of fuel for some sort of extended mission but it'll be trade off between a really long extended mission but at higher closest approach, some more deep dips, or a medium length extended mission with the same normal closest approach (~150km) but no deep dips. The science team will have to fight this out if we get the opportunity for an extended mission. Maybe I'll suggest we decide via a Starcraft 2 elimination tournament.

jccwrt2 karma

Follow-on question. Would the mission team be comfortable with doing dips even deeper than 125km, or would MAVEN not survive going that deep?

maven2mars2 karma

I think 125km is lowest the aerobraking specialists feel comfortable with. Lower would be cool but frankly 125 km is really perfect for our interests in the ionosphere. Any lower and you're starting to talk about a "real" atmosphere. The Solar Wind erosion won't affect stuff that low until it got pushed up higher.

mars_alive4 karma

You said that you were going to 'do our best to count all the particles escaping from the planet at any given moment in space and time and then add that all up and see if it makes enough escaping atmosphere over 4 billion years', but isn't there a risk of a large margin of error if you just extrapolate from the escape rate today? Doesn't it depend on the strength of the magnetic field and also the behaviour of the solar wind over Mars' history?

maven2mars6 karma

Yup, that's very insightful. So, we'll also have to carefully know how and when the magnetic field went away (gradually, in patches, etc.). We'll also need to know the behavior of the Sun and the Solar Wind over all that time. So, we'll have to look at other stars at various stages of their evolution and try to use that to guide us. This is all part of our science team's discussions and plans.

mars_alive4 karma

If MAVEN does establish that Mars lost its atmosphere via the solar wind, how might that inform future missions, e.g. Mars Sample Return?

maven2mars9 karma

We hope to establish that what caused Mars to change from habitability to desolation is the Solar Wind. So once we understand if that's what happened, we'll be better informed about the geological processes occurring on the ground and thus where to do sample return.

habitmelon3 karma

Is it possible to restore Mars' global magnetic field (assuming it had one like Earth's originally)?

maven2mars4 karma

Unlikely. The global magnetic field at Mars probably stopped because the internal dynamo stopped which probably means the core froze out. Now I know that you're thinking of that movie with nukes in the core but that was not exactly cutting edge science advising in that movie.

anonynamja3 karma

If you terraform mars, don't send roaches.

maven2mars6 karma

So many banelings.

Universu3 karma

How did the MAVEN program came about?

maven2mars6 karma

There had been this open question for a while about how the martian atmosphere got to where it is. My understanding is that Bruce Jakosky (PI), Bob Lin (former deputy PI, now deceased), and Janet Luhmann (current deputy PI) where talking about the question and thought they could put together a realistic proposal to address the question. I wasn't there so I don't know the details but that was about 10 years ago and here we are ready to launch to Mars.

tugreenwave3 karma

For those not in the know, PI stands for Principal Investigator.

maven2mars4 karma

Yeah, sorry. I try to avoid acronyms but it's hard to remember plus it's hard to type so much. :)

zapattavilla3 karma

Will you use IA to analyze data? If yes, which one?

maven2mars6 karma


Universu3 karma

Is the Red Dragon proposal still being considered?

maven2mars6 karma

Not familiar with that one.

Unrelated_Incident2 karma

Hi Jared. I've heard that Russia is developing a nuclear powered space craft. Is there any chance of the US working on something similar? What would be the benefits and major hurdles for such a project?


maven2mars3 karma

MSL is nuclear powered. There are certainly efforts at NASA to work on more refined engines but I have no expertise in this at all. I'd literally start clicking links on wikipedia if I tried to answer your question any further.

Universu2 karma

What is the exact time of arrival of MAVEN on Mars?

maven2mars7 karma

MAVEN will enter Martian orbit on or around Sept. 22, 2014 (depending on exact launch date). Six orbital insertion thrusters, each with 45 pounds of thrust, will fire for 38 minutes to slow the craft and establish a 35-hour orbit at a 75-degree inclination. During this phase, the closest point in the orbit to the planet (periapsis) is 236 miles (380 km).

During a five-week “commissioning phase,” MAVEN will carry out five maneuvers to settle into its final, 4.5-hour scientific mapping orbit. The spacecraft will also power up and test all instruments before commencing its scientific mission. Spacecraft booms will be deployed during the commissioning phase.

maven2mars5 karma

I think we arrive Sept. 22, 2014 assuming our launch happens as expected on Monday. Someone with google-fu and doing less typing than me might be able to look that one up to confirm that for me. I don't know the time -- it might depend slightly on exactly how the rocket burns go.

Universu3 karma

Who decide dates of arrival of September 22? any special commemoration to it? like Pathfinder or Juno date of July 4? Thanks

maven2mars6 karma

It's the soonest we can get there after our launch given our fuel budget. We're anxious to get started our science!

lasergrad2 karma

What kind of laser- or optics-related development went into the mission? I can imagine many instances, but I do not want to limit/bias your answer!

(Also, is there an open position in lasers/optics/photonics in the mission / group you're working? I defend my dissertation in 11 days!)

maven2mars6 karma

I can't speak for all the instruments and especially not for the spacecraft. But for the magnetometer (the instrument I helped develop), we do have an optical cube to help align the instrument but its otherwise very light (hah) on optics. In general, the mission has few cameras, etc. -- it's mostly particle spectrometers.

But, yeah you should definitely check out jobs at NASA. There's the NASA postdoctoral program that hires a fair number of people. You can find it on the web.

karmisson2 karma


maven2mars8 karma

I was only furloughed for a couple of days because we were allowed to resume work b/c we are a backup relay for the rovers so we would need to make our launch window. During my days "off", I mostly hung out with my new-born daughter.

you_are_temporary2 karma

What is your degree in? What about space extraction will be the very first thing to have an impact on people's personal lives?

maven2mars6 karma

Physics. Extraction or Exploration? I think it'll be while before extraction has an effect. Probably won't effect lives until those lives are in space.

Arxivist2 karma

Looking to the future what other science objectives do we have on Mars? Curiosity determined that it once had conditions favorable to life, and MAVEN will determine what happened to these conditions.

What objective is next?

maven2mars4 karma

NASA's current plan is send another rover in 2020 to gather particularly interesting geological samples, store them somewhere central, and then hope to have another, even more future mission go pick them up to take them home to Earth to analyze them for signs of past life and habitability conditions

BEEfStU_1402 karma

Can you please provide proof in the description of your post?

maven2mars8 karma

Ok, tweets from me (Jared) and the official mission feed. Thanks for checking. :)

maven2mars5 karma

Proof in the description now.

ThaNinjaGinga2 karma

I'm a 15 year old student, what would you say are the chances that by the time I join the workforce and start my career that I could be a Martian Astronaut?

maven2mars2 karma

Low but not impossible. On the other hand, I think it's very likely that you could a scientist or engineer working for a space agency doing cool space missions in 2028 when you're 30 if that's what you choose.

Mahikluigi2 karma

Where will the launch be visible from? Also, how did you get your job?

maven2mars2 karma

Not sure how far the launch will be visible from. Not as far a shuttle but something like that. Got job by doing grad school work on similar topic.

TRUBored2 karma

What's the status of project HOYVEN

maven2mars2 karma

I'm guessing language joke since MAVEN has a meaning in Yiddish I think.

Roderick1112 karma

Will MAVEN be able to detect methane (if any) in the Martian atmosphere?

maven2mars2 karma

No. The methane (if it's there) is produced near ground level and would be broken up by the time it reaches the ionospheric altitudes where we could detect it. We mostly have instruments to see things directly and locally whereas other instruments (e.g. IR spectrometers, etc.) on other missions see things remotely like a telescope.

SelectricSimian2 karma

What are your thoughts on terraforming? Do you think it will ever be technologically feasible to return mars to its previous warm, wet state?

maven2mars3 karma

Good question but see some of my previous responses.

Metalman11ty12 karma

This sounds awesome I'm glad I came across this. Here's my question:

What is Your individual role in this mission (Any of you guys answering questions)

maven2mars4 karma

I'm a science team member. I specifically helped develop the magnetometer instrument and I will help distribute this data to the community at large and I myself will also use the data to do science analysis.

WhitneyRobbens2 karma

In all seriousness, what do you think the chances are of a manned mission to Mars? How long would it take to prepare for? Even if it is a one way mission? If so... how long before we could have the technology to make such a thing possible?

It's not just because I think we should be colonizing our solar system,

...not because my inner 9 year old would squeeee with happiness,

...not just for the dream of space travel and exploration,

...and not just because I'm a huge Star Trek/Firefly/ Space loving geek,

I think it is something that we as a species are destined to do, and for it to happen in my life time would be amazing.

maven2mars2 karma

I think it's very plausible that we could send humans to Mars but that it's very expensive so it's really a political/societal question. It's certainly the stated goal of the current NASA administration.

ukcreation2 karma

Kim Stanley Robinson's Mars Trilogy first really made me passionate about Mars and generally the idea of humanity stepping off Earth, but is the idea that we could impact the atmosphere of Mars to make it more habitable, even to a minor degree, just science fiction or could we one day return oceans to Mars' surface?

maven2mars3 karma

Terraforming is probably not literally impossible it's a geological scaled task in time and energy so not something that I would expect to happen soon or necessarily ever. We'd have to have a tremendous societal will to do it. But i agree it's a really cool idea and I love Robinson's trilogy too.

Jilleh-bean1 karma

Do you think humans will discover that we're not alone in the universe during our lifetime?

maven2mars2 karma

I don't know. The Fermi paradox does make one think.

Vexxus1 karma

My astronomy professor just left yesterday to go work with you guys! Just want to say good luck, and thank you!

maven2mars2 karma

Awesome. I'll see him tomorrow probably at the science team meeting.

Dsvkb1 karma

How does pro wrestler Maven feel about his name being on the rocket? In all seriousness, I hope the mission goes as well as possible!

maven2mars3 karma


rickydelap1 karma

What is different from this mission to the one that is happening right now?

maven2mars4 karma

This one is an orbiter unlike the rovers that have recently been very much in the news. Our science objective is to understand the upper atmosphere of Mars and how it's erosion by the Solar Wind might have led to the drastic climate change we see with our other assets (rovers and orbiters).