Valtteri Bottas raced 78 times for Williams, finishing on the podium nine times

Valtteri Bottas faces the opportunity and challenge of his life following his switch to Mercedes for 2017.

After four seasons of solid performances with Williams, the 27-year-old Finn has been rewarded with every driver's dream - a seat with the best team in Formula 1.

Barring a remarkable slip in form for Mercedes, Bottas will morph from being an occasional podium visitor to a race-winner and possibly title contender this year.

But in new team-mate Lewis Hamilton, Bottas faces an adversary far beyond anything he has experienced so far. How he measures up will likely define the rest of his career.

Why did Mercedes pick Bottas?

Bottas might not be the most exciting of choices for Mercedes. Fans around the world would have loved to see Hamilton battle McLaren's Fernando Alonso again, or take on Red Bull's Daniel Ricciardo or Max Verstappen, or Ferrari's Sebastian Vettel. But his appeal to Mercedes F1 boss Toto Wolff is obvious.

Bottas is Wolff's attempt to find a like-for-like replacement for German Nico Rosberg, who dropped Mercedes in the mire by announcing his retirement last year, five days after clinching his first world title. And it's not just about their blond hair or Finnish ancestry.

Valtteri Bottas 'hungry' for success at Mercedes

Bottas shares many of Rosberg's characteristics. Both are calm, unobtrusive characters, who are generally pliable and understanding in terms of working with the team and lack the demanding nature of a Hamilton or Alonso.

On the track they are consistent, largely error-free performers. And Bottas has proved himself a resilient and hard racer.

Wolff should - he hopes - be able to plug Bottas in and carry on pretty much where Mercedes left off in the past few years.

How quick is Bottas?

Wolff rates Bottas extremely highly. But now he has joined Mercedes, the big question is: how good is he?

There have been flashes of brilliance - such as qualifying third in the wet in an uncompetitive Williams in Canada in 2013 - that suggest a real talent.

And overall, the general perception is Bottas' record against Felipe Massa at Williams over the past three years is similar to Alonso's against the Brazilian at Ferrari before that.

But the facts do not bear that out. While Bottas and Alonso beat Massa in both qualifying and races, the Spaniard's advantage over the Brazilian was significantly bigger.

Based on these comparisons, Hamilton should be faster than Bottas next season

Directly comparing the data suggests Bottas is as much as 0.2-0.3 seconds per lap slower than Alonso and considerably less effective in races.

Neither Massa nor Bottas have been team-mates to Hamilton. But Alonso has - at McLaren in 2007. They finished tied on points, with four wins each, and Hamilton edged qualifying by the tiniest of margins. By any measure, it was - and is - very difficult to separate Hamilton and Alonso.

If 2017 follows the trend of those results, Hamilton can be expected to be comfortably quicker than Bottas.

Perhaps more surprising is that those comparisons suggest that not only is Bottas not a match for Alonso and Hamilton, but he might not equal Rosberg either.

However, drivers' form does not always directly translate across teams and rivals in as linear a fashion as might be expected.

It is up to Bottas to prove the comparisons wrong and grab the opportunity with both hands.

Last season, Bottas (right) out-qualified team-mate Massa 17 times in 21 races

A philosophical reason behind Bottas

Bottas was always the only realistic option once Wolff decided against Mercedes junior Pascal Wehrlein. Bottas is quick, dependable, has had a management relationship with Wolff, and raced for a team that had Mercedes engines, and with which a deal therefore might more easily be done.

All the A-list drivers - Alonso, Ricciardo, Verstappen and Vettel - were not available. They are under contract to leading teams that would have been left in a similar position to Mercedes had they allowed them to leave.

But if they had been available, Wolff may not have wanted most of them anyway.

Part of the decision to sign the same type of driver as Rosberg was a desire to retain the team dynamic.

Rosberg and Hamilton worked for Mercedes because only one of them saw it as a right and expectation to be in front. Spoken or not, there was a natural order. They were, as one senior Mercedes insider once put it, "a great driver and a very good one".

Nico Rosberg and Lewis Hamilton clashed on numerous occasions and Mercedes will be hoping the same does not happen with Bottas and Hamilton

This is a way of keeping the rivalry manageable and under control without the need for too much team interference.

The faster driver - Hamilton - knows he will win most of the time as long as he performs at his best. And the other one - a different personality - is able to keep defeat in perspective more easily when it happens.

As Wolff put it on Monday: "Valtteri shares our values and passion, and he's modest, humble and hard-working."

But there is a possibility the team dynamic will change anyway.

How might it affect Hamilton?

Daimler chairman Dieter Zetsche recently provided an amusing insight into Mercedes' relationship with Hamilton.

Talking to Autocar magazine about how he heard the news of Rosberg's retirement, Zetsche said: "I was stepping out of the shower lacking any clothes and my phone was ringing. And I saw it was Toto and I thought: 'Oh, again something with Lewis!'"

His remarks confirm the open secret that Hamilton is not an easy driver to manage.

Like all drivers of his stature, Hamilton can be awkward over PR appearances and other such matters that are expected of drivers but they find tiresome. And he has repeatedly bucked against the authority of the team.

In ignoring orders to speed up while 'backing' Rosberg into rivals in the title-deciding race in Abu Dhabi, Hamilton was metaphorically sticking two fingers up to team management.

Wolff initially said he would consider what actions to take. Then, Hamilton spoke of feeling "disrespected" by that call. Following Rosberg's retirement, Wolff and soon-to-leave technical boss Paddy Lowe said the orders should not have been issued.

Throughout last season, Hamilton repeatedly brought up the reliability disparity that was giving Rosberg an advantage in their title battle.

Hamilton's 2016 title bid was hindered by reliability problems but he is favourite for the 2017 championship

In Malaysia - after his engine failed while he was leading, costing him the championship lead and, as it turned out, the title - he went as far as saying "something or someone doesn't want me to win this year".

Many interpreted that wrongly as a suggestion there was a conspiracy in the team. But even as a reference to bad luck or divine intervention, it is a statement that causes Mercedes problems.

After Hamilton refused to take questions in a news conference at the Japanese Grand Prix last year, Wolff called such incidents "collateral damage", and insisted "his performances in the car justify" it.

But sometimes - if very rarely - Hamilton is not phenomenal in the car. And some in F1 question his 'off' weekends and occasional problematic behaviour as directly linked to his decision to pursue a Hollywood lifestyle. This, they argue, restricts his ability to perform at his absolute best all the time.

They see his jetting back and forth to the US as a lack of focus and blame it for weekends such as those in Baku and Singapore last year, where Hamilton quite patently, and for reasons that are not clear, just did not bring his 'A game'.

And they believe it is facilitated by Mercedes' choice of a team-mate Hamilton knows he can handle.

Wolff and Hamilton, meanwhile, insist it is the freedom Mercedes give him to be himself that allows him to perform at his peak - and everyone has a bad day once in a while.

And it seems more likely that the 'off' weekends are just part of him, and related to specific aspects of car behaviour, a set-up he cannot get right, or which he refuses to adapt to because he feels it is not working for him.

Valtteri Bottas has some big boots to fill, replacing world champion Nico Rosberg as Lewis Hamilton's Mercedes team-mate

His occasional unpredictability is one of the reasons Mercedes need a strong team-mate for Hamilton - and not just to score regular points in the constructors' championship, the main reason Bottas was preferred over Wehrlein.

While Rosberg was not on Hamilton's level as a driver, he was close enough to give Mercedes a viable alternative as a counter-balance.

The likelihood is Bottas will slot in and be - at least - a direct Rosberg replacement. While that is the case, Mercedes might not want a driver with a talent comparable to Hamilton - and the attitude that tends to come with it.

But if he can't challenge Hamilton regularly, Wolff might, for a number of reasons, wonder whether signing another superstar alongside Hamilton is not such a bad idea after all.

Vettel and Alonso, both out of contract at the end of the year, will be watching this with interest.

Bottas will go into Mercedes aiming to win races and titles, but he will be as aware as anyone of the challenge facing him.

Hamilton will likely already feel emboldened, his position strengthened by Rosberg's departure, and a weaker team-mate would only enhance that feeling.

View the 2017 F1 race calendar here