Un­de­tected-planet idea back in fo­cus

Northwest Arkansas Democrat-Gazette - - NORTHWEST ARKANSAS - JAIME ADAME

FAYET­TEVILLE — Finding an undis­cov­ered planet in the so­lar sys­tem isn’t easy, said as­tro­physi­cist Daniel Whit­mire.

In the vast­ness of sky, “the prob­lem is, you don’t know where to look,” said Whit­mire.

His re­search in the 1980s while work­ing at the Univer­sity of Louisiana at Lafayette de­scribed the pos­si­bil­ity of an undis­cov­ered world or­bit­ing the sun.

Such a planet would be more than just an im­por­tant as­tro­nom­i­cal dis­cov­ery, ac­cord­ing to an idea put for­ward by Whit­mire and col­league John Matese. Their work de­scribed a planet where the or­bit around the sun took much longer to com­plete than Earth’s or any known planet, and whose path var­ied in a pre­dictable way so that ev­ery sev­eral mil­lions of years it dis­lodged clus­ters of dis­tant comets.

Shaken loose by the hid­den planet’s grav­ity as it ap­proached, the comets would then break away in all di­rec­tions — in­clud­ing to­ward Earth.

“In hind­sight, the odds were not too good in finding it,” said the soft-spo­ken Whit­mire, 74 and now a math in­struc­tor at the Univer­sity of Arkansas, Fayet­teville. “Now, to­day, the odds are much bet­ter.”

Decades af­ter Whit­mire’s ideas gained pop­u­lar at­ten­tion and were part of a Time mag­a­zine cover story, other as­tro­physi­cists have in­de­pen­dently de­clared new ideas about undis­cov­ered plan­ets at the fringes of the so­lar sys­tem. Vol­un­teers and sci­en­tists alike are seek­ing to di­rectly ob­serve what for now re­mains un­proven.

But un­like their work, Whit­mire ties to­gether the pos­si­bil­ity of an un­seen planet and the idea of catas­tro­phe on Earth.

He rea­sons that some comets shaken loose would strike Earth and cause global harm.

His the­o­ret­i­cal re­search is based “on the need to find an as­tro­nom­i­cal ex­pla­na­tion for pe­ri­odic mass ex­tinc­tions,”

Whit­mire said, with the next comet shower event pre­dicted in his hy­poth­e­sis about 16 mil­lion years away. “You can re­lax,” he said. Some sci­en­tists told the Arkansas Demo­crat-Gazette they doubt de­tails of ex­tinc­tion that led Whit­mire to de­velop his hy­poth­e­sis, and Whit­mire ac­knowl­edged dis­agree­ment among pa­le­on­tol­o­gists.

When it comes to the new work by as­tro­physi­cists on pos­si­ble plan­ets, how­ever, noth­ing rules out what he pro­posed decades ago, he said.

In aca­demic journal Na­ture, Whit­mire and Matese laid out an idea for a “Planet X” that in­ter­acts grav­i­ta­tion­ally ev­ery 26 mil­lion years with ob­jects in what is known as the Kuiper belt, a re­gion be­yond Nep­tune. Whit­mire said the best es­ti­mate now is that this hap­pens ev­ery 27 mil­lion years.

The Planet X hy­poth­e­sis states that it ro­tates around the sun about ev­ery 1,000 years. But as it moves, its or­bit “re­ori­ents it­self very slowly, over mil­lions of years,” Whit­mire said.

Twice dur­ing what’s known as a pre­ces­sion, a pe­riod that Whit­mire de­scribed as last­ing 54 mil­lion years, it causes comets in the Kuiper belt to be­come dis­lodged from their typ­i­cal or­bital pat­terns in space.

“It plows into, grav­i­ta­tion­ally speak­ing, some comets and scat­ters them all over the place,” Whit­mire said.

Planet X likely would be “around one Earth mass,” though it could be up to five times as big, he said.

Last year, aca­demic journal Monthly No­tices of the Royal As­tro­nom­i­cal So­ci­ety pub­lished an up­date from Whit­mire in light of new work done by other as­tro­physi­cists.

At the time he and Matese first pub­lished their ideas, “there was a lot of skep­ti­cism” about the ex­is­tence of an­other planet in the so­lar sys­tem, Whit­mire said.

“That’s been grad­u­ally chang­ing over the years,” he said.

Cal­i­for­nia In­sti­tute of Tech­nol­ogy re­searchers last year de­scribed ev­i­dence point­ing to what they re­fer to as Planet Nine, roughly 10 times the mass of Earth. Kon­stantin Baty­gin and Mike Brown an­nounced their find­ings about a dis­tant planet, with Brown telling The New York Times, “we are pretty sure there’s one out there.”

Whit­mire called the re­searchers’ Planet Nine work “truly main­stream.”

“You’ve got ev­ery as­tronomer in the world look­ing for it,” said Whit­mire.

The Univer­sity of Ari­zona last month an­nounced that re­searchers also posit the ex­is­tence of an un­seen planet, per­haps less mas­sive than Earth.

Whit­mire said he moved to North­west Arkansas for fam­ily rea­sons, and his in­ter­est in space goes back to his boy­hood in Ge­or­gia. He be­came en­thralled by an aunt’s en­cy­clo­pe­dia and its in­for­ma­tion about the plan­ets, he said.

“My par­ents were not highly ed­u­cated. They didn’t go to col­lege,” Whit­mire said. At ev­ery visit to his aunt’s, “Boy, I’d go in there and dig that out, read ev­ery­thing” Whit­mire said.

Sci­en­tists de­scribe the so­lar sys­tem dif­fer­ently, com­pared with decades past. Eight plan­ets have been ob­served, with Nep­tune the far­thest away. Sci­en­tists once in­cluded Pluto as a ninth planet be­fore tak­ing note of how small it is.

Whit­mire said he also col­lab­o­rated on an­other re­search pa­per in the 1980s that pro­posed a larger planet some­times de­scribed as “Neme­sis.”

“The Neme­sis model is not 100 per­cent re­jected yet,” Whit­mire said.

But data re­lat­ing to the pos­si­bil­ity of pe­ri­odic mass ex­tinc­tions have not sup­ported the de­tails of such a “Neme­sis” planet, Whit­mire said.

He re­ferred to the work of Univer­sity of Kansas physics and as­tron­omy pro­fes­sor Adrian Melott.

Melott said he’s found “strong ev­i­dence” that, go­ing back about 500 mil­lion years, “there is a pat­tern of re­cur­ring [ex­tinc­tion] events ev­ery 27 mil­lion years.”

“Whit­mire’s ex­pla­na­tion is the only one that does not have a se­ri­ous prob­lem,” said Melott, who has col­lab­o­rated with Richard Bam­bach, a pa­le­o­bi­ol­ogy re­search as­so­ci­ate at the Na­tional Mu­seum of Nat­u­ral His­tory.

Pa­le­on­tol­o­gists de­scribe mass ex­tinc­tions as the dying off of species within a rel­a­tively short pe­riod of time. Some dis­agreed about the de­tails of such global events.

Gerta Keller, a Prince­ton geo­sciences pro­fes­sor, in an email said that “by the late 1980s this pe­ri­od­ic­ity idea was thor­oughly dis­cred­ited.”

Others spoke less harshly, but said it’s far from set­tled.

“I think the big prob­lem is, it de­pends on how you de­fine the term ‘mass ex­tinc­tion,’” said David Jablon­ski, a pro­fes­sor in the geo­phys­i­cal sciences depart­ment at the Univer­sity of Chicago.

In pa­le­on­tol­ogy, “ev­ery­one agrees that there were f ive re­ally ma­jor ones,” Jablon­ski said.

Those events were not spaced out in iden­ti­cal time in­ter­vals, he said, but analy­ses take into ac­count “a whole fam­ily of smaller pulses,” he said. Meth­ods of dat­ing ge­o­log­i­cal ev­i­dence im­prove, lead­ing to bet­ter — but shift­ing — in­for­ma­tion, he said.

“It’s a very dif­fi­cult, sub­tle prob­lem,” Jablon­ski said, call­ing it “not ob­vi­ous” that mass ex­tinc­tions took place at reg­u­lar in­ter­vals.

Jonathan Payne, a Stanford pro­fes­sor of ge­o­log­i­cal sciences, said there is “at least some ev­i­dence for cyclic­ity in ex­tinc­tions.”

Sci­en­tists have found ev­i­dence of an im­pact event co­in­cid­ing with a mass ex­tinc­tion tak­ing place at the end of what’s known as the Cre­ta­ceous Pe­riod, he said.

For other mass ex­tinc­tions, how­ever, “the best ev­i­dence right now is not point­ing to­wards an im­pact event” as their cause, Payne said.

As­tro­physi­cists look­ing at the so­lar sys­tem de­scribed both in­di­rect data sug­gest­ing an­other planet and ef­forts aimed at di­rect ob­ser­va­tion.

This Fe­bru­ary, NASA called for vol­un­teers to help look through images cap­tured by the agency’s Wide­field In­frared Sur­vey Ex­plorer mis­sion.

Marc Kuch­ner, a NASA as­tro­physi­cist, is prin­ci­pal in­ves­ti­ga­tor for the Back­yard Worlds: Planet 9 project.

Over the past 10 years or so, “just like cam­eras on your cell­phone have been get­ting big­ger, cam­eras in tele­scopes have also been get­ting big­ger, and it’s opened up new ar­eas of sci­ence that peo­ple haven’t been able to con­sider be­fore,” Kuch­ner said.

The Univer­sity of Ari­zona re­searchers an­nounced last month a pos­si­ble planet af­fect­ing ob­jects in the Kuiper belt.

“There’s a long his­tory of try­ing to go look at ob­jects in the so­lar sys­tem and see if there are un­ex­plained grav­i­ta­tional ef­fects on those ob­jects that could be associated with some­thing we haven’t dis­cov­ered yet,” said Kat Volk, a Univer­sity of Ari­zona post­doc­toral re­searcher, ex­plain­ing her work with Renu Mal­ho­tra, a Univer­sity of Ari­zona plan­e­tary sciences pro­fes­sor.

Af­ter ob­serv­ing an un­ex­plained tilt to ob­jects in the Kuiper belt, “we think an un­seen planet is the most likely ex­pla­na­tion,” Volk said.

She said that it can be dif­fi­cult to ob­serve an ob­ject if it lies in a por­tion of the sky that falls within what’s called the ga­lac­tic plane, which is where the Milky Way in a dark night sky can be seen.

The so­lar sys­tem lies in the Milky Way galaxy, and Volk said it can be very dif­fi­cult to “pick out these fainter mov­ing ob­jects” in a crowded, starry back­ground.

Mo­tion of ob­jects in the so­lar sys­tem is de­tected by com­par­ing images taken at dif­fer­ent time in­ter­vals, re­quir­ing pa­tience to de­tect a far­away ob­ject that ap­pears to move more slowly against its back­ground, Volk said.

She also said that “a very big area of sky” re­mains that has yet to be sur­veyed thor­oughly.

The NASA Back­yard Worlds project would not un­cover a planet smaller than Nep­tune, Kuch­ner said. Nep­tune has about 17 times as much mass as Earth, ac­cord­ing to NASA.

Dis­cov­ery of a new planet in the so­lar sys­tem “would end up in text­books,” said Kuch­ner. “It would end up in ev­ery chil­dren’s book on the so­lar sys­tem.”

An­other NASA project, the Large Synop­tic Sur­vey Te­le­scope, or LSST, is un­der con­struc­tion in Chile. It is ex­pected to be­gin op­er­a­tions in 2022, Ivy Ku­pec, a NASA pub­lic af­fairs spe­cial­ist, said in an email.

“LSST should be sen­si­tive to, I think all of these dif­fer­ent po­ten­tial plan­ets,” Kuch­ner said. “If LSST doesn’t find it, then it prob­a­bly doesn’t ex­ist,” Kuch­ner said. Volk said she thinks “we’ll get an an­swer within the next decade.”

Whit­mire holds on to the idea that the planet he hy­poth­e­sized about more than 30 years ago could be ob­served di­rectly. Many spec­u­la­tive the­o­ries get shot down quickly by other sci­en­tists, he said, with Planet X still re­main­ing a pos­si­bil­ity.

“Planet Nine is still not a done deal at all, and ours is also not a done deal,” said Whit­mire. “It’s just that ours has been around for all this time.”

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